diff --git a/composer.json b/composer.json
index 691ceae..db421a1 100644
--- a/composer.json
+++ b/composer.json
@@ -33,13 +33,18 @@
         "php": "^7.4 || ^8.0",
         "sabre/xml": "^4.0",
         "nesbot/carbon": "^2.72 || ^3.11",
-        "doctrine/collections": "^1.8 || ^2.0"
+        "doctrine/collections": "^1.8 || ^2.0",
+        "ext-fileinfo": "*",
+        "ext-libxml": "*"
     },
     "require-dev": {
         "squizlabs/php_codesniffer": "^3.7",
         "phpstan/phpstan": "^1.10",
         "brianium/paratest": "^6.11",
-        "phpunit/phpunit": "^9.6"
+        "phpunit/phpunit": "^9.6",
+        "ext-dom": "*",
+        "ext-json": "*",
+        "ext-soap": "*"
     },
     "autoload": {
         "psr-4": {
diff --git a/src/AccountingParty.php b/src/AccountingParty.php
index 4e251b9..8409f3f 100644
--- a/src/AccountingParty.php
+++ b/src/AccountingParty.php
@@ -11,12 +11,12 @@
 
 class AccountingParty implements XmlSerializable, XmlDeserializable
 {
-    private $supplierAssignedAccountID;
-    private $party;
-    private $accountingContact;
+    private ?string $supplierAssignedAccountID = null;
+    private ?Party $party = null;
+    private ?Contact $accountingContact = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getSupplierAssignedAccountId(): ?string
     {
@@ -24,7 +24,7 @@ public function getSupplierAssignedAccountId(): ?string
     }
 
     /**
-     * @param string $supplierAssignedAccountID
+     * @param string|null $supplierAssignedAccountID
      * @return static
      */
     public function setSupplierAssignedAccountId(?string $supplierAssignedAccountID)
@@ -34,7 +34,7 @@ public function setSupplierAssignedAccountId(?string $supplierAssignedAccountID)
     }
 
     /**
-     * @return Party
+     * @return Party|null
      */
     public function getParty(): ?Party
     {
@@ -42,7 +42,7 @@ public function getParty(): ?Party
     }
 
     /**
-     * @param Party $party
+     * @param Party|null $party
      * @return static
      */
     public function setParty(?Party $party)
@@ -52,7 +52,7 @@ public function setParty(?Party $party)
     }
 
     /**
-     * @return ?Contact
+     * @return Contact|null
      */
     public function getAccountingContact(): ?Contact
     {
@@ -60,7 +60,7 @@ public function getAccountingContact(): ?Contact
     }
 
     /**
-     * @param Contact $accountingContact
+     * @param Contact|null $accountingContact
      * @return AccountingParty
      */
     public function setAccountingContact(?Contact $accountingContact): AccountingParty
@@ -99,7 +99,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -109,7 +109,6 @@ public static function xmlDeserialize(Reader $reader)
         return (new static())
             ->setParty($keyValues[Schema::CAC . 'Party'] ?? null)
             ->setSupplierAssignedAccountId($keyValues[Schema::CBC . 'SupplierAssignedAccountID'] ?? null)
-            ->setAccountingContact($keyValues[Schema::CBC . 'AccountingContact'] ?? null)
-        ;
+            ->setAccountingContact($keyValues[Schema::CBC . 'AccountingContact'] ?? null);
     }
 }
diff --git a/src/AdditionalDocumentReference.php b/src/AdditionalDocumentReference.php
index 73d014a..88f50ad 100644
--- a/src/AdditionalDocumentReference.php
+++ b/src/AdditionalDocumentReference.php
@@ -11,14 +11,14 @@
 
 class AdditionalDocumentReference implements XmlSerializable, XmlDeserializable
 {
-    private $id;
-    private $documentType;
-    private $documentTypeCode;
-    private $documentDescription;
-    private $attachment;
+    private ?string $id = null;
+    private ?string $documentType = null;
+    private $documentTypeCode = null;
+    private ?string $documentDescription = null;
+    private ?Attachment $attachment = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getId(): ?string
     {
@@ -26,7 +26,7 @@ public function getId(): ?string
     }
 
     /**
-     * @param string $id
+     * @param string|null $id
      * @return static
      */
     public function setId(?string $id)
@@ -36,7 +36,7 @@ public function setId(?string $id)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getDocumentType(): ?string
     {
@@ -44,7 +44,7 @@ public function getDocumentType(): ?string
     }
 
     /**
-     * @param string $documentType
+     * @param string|null $documentType
      * @return static
      */
     public function setDocumentType(?string $documentType)
@@ -62,7 +62,7 @@ public function getDocumentTypeCode()
     }
 
     /**
-     * @param int|string $documentTypeCode
+     * @param int|string|null $documentTypeCode
      * @return static
      */
     public function setDocumentTypeCode($documentTypeCode)
@@ -72,7 +72,7 @@ public function setDocumentTypeCode($documentTypeCode)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getDocumentDescription(): ?string
     {
@@ -80,7 +80,7 @@ public function getDocumentDescription(): ?string
     }
 
     /**
-     * @param string $documentDescription
+     * @param string|null $documentDescription
      * @return static
      */
     public function setDocumentDescription(?string $documentDescription)
@@ -90,7 +90,7 @@ public function setDocumentDescription(?string $documentDescription)
     }
 
     /**
-     * @return Attachment
+     * @return Attachment|null
      */
     public function getAttachment(): ?Attachment
     {
@@ -98,7 +98,7 @@ public function getAttachment(): ?Attachment
     }
 
     /**
-     * @param Attachment $attachment
+     * @param Attachment|null $attachment
      * @return static
      */
     public function setAttachment(?Attachment $attachment)
@@ -144,7 +144,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -156,7 +156,6 @@ public static function xmlDeserialize(Reader $reader)
             ->setDocumentType($keyValues[Schema::CBC . 'DocumentType'] ?? null)
             ->setDocumentTypeCode($keyValues[Schema::CBC . 'DocumentTypeCode'] ?? null)
             ->setDocumentDescription($keyValues[Schema::CBC . 'DocumentDescription'] ?? null)
-            ->setAttachment($keyValues[Schema::CAC . 'Attachment'] ?? null)
-        ;
+            ->setAttachment($keyValues[Schema::CAC . 'Attachment'] ?? null);
     }
 }
diff --git a/src/AdditionalItemProperty.php b/src/AdditionalItemProperty.php
index 1902097..114578f 100644
--- a/src/AdditionalItemProperty.php
+++ b/src/AdditionalItemProperty.php
@@ -17,11 +17,11 @@
  */
 class AdditionalItemProperty implements XmlSerializable, XmlDeserializable
 {
-    private $name;
-    private $value;
+    private ?string $name = null;
+    private ?string $value = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getName(): ?string
     {
@@ -29,7 +29,7 @@ public function getName(): ?string
     }
 
     /**
-     * @param string $name
+     * @param string|null $name
      * @return static
      */
     public function setName(?string $name)
@@ -39,7 +39,7 @@ public function setName(?string $name)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getValue(): ?string
     {
@@ -47,7 +47,7 @@ public function getValue(): ?string
     }
 
     /**
-     * @param string $value
+     * @param string|null $value
      * @return static
      */
     public function setValue(?string $value)
diff --git a/src/Address.php b/src/Address.php
index 0f65433..e240d97 100644
--- a/src/Address.php
+++ b/src/Address.php
@@ -12,17 +12,17 @@
 
 class Address implements XmlSerializable, XmlDeserializable
 {
-    private $streetName;
-    private $additionalStreetName;
-    private $buildingNumber;
-    private $cityName;
-    private $postalZone;
-    private $countrySubentity;
-    private $addressLines = [];
-    private $country;
+    private ?string $streetName = null;
+    private ?string $additionalStreetName = null;
+    private ?string $buildingNumber = null;
+    private ?string $cityName = null;
+    private ?string $postalZone = null;
+    private ?string $countrySubentity = null;
+    private array $addressLines = [];
+    private ?Country $country = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getStreetName(): ?string
     {
@@ -30,7 +30,7 @@ public function getStreetName(): ?string
     }
 
     /**
-     * @param string $streetName
+     * @param string|null $streetName
      * @return static
      */
     public function setStreetName(?string $streetName)
@@ -40,7 +40,7 @@ public function setStreetName(?string $streetName)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getAdditionalStreetName(): ?string
     {
@@ -48,7 +48,7 @@ public function getAdditionalStreetName(): ?string
     }
 
     /**
-     * @param string $additionalStreetName
+     * @param string|null $additionalStreetName
      * @return static
      */
     public function setAdditionalStreetName(?string $additionalStreetName)
@@ -58,7 +58,7 @@ public function setAdditionalStreetName(?string $additionalStreetName)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getBuildingNumber(): ?string
     {
@@ -66,7 +66,7 @@ public function getBuildingNumber(): ?string
     }
 
     /**
-     * @param string $buildingNumber
+     * @param string|null $buildingNumber
      * @return static
      */
     public function setBuildingNumber(?string $buildingNumber)
@@ -76,7 +76,7 @@ public function setBuildingNumber(?string $buildingNumber)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getCityName(): ?string
     {
@@ -84,7 +84,7 @@ public function getCityName(): ?string
     }
 
     /**
-     * @param string $cityName
+     * @param string|null $cityName
      * @return static
      */
     public function setCityName(?string $cityName)
@@ -94,7 +94,7 @@ public function setCityName(?string $cityName)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getPostalZone(): ?string
     {
@@ -102,7 +102,7 @@ public function getPostalZone(): ?string
     }
 
     /**
-     * @param string $postalZone
+     * @param string|null $postalZone
      * @return static
      */
     public function setPostalZone(?string $postalZone)
@@ -112,7 +112,7 @@ public function setPostalZone(?string $postalZone)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getCountrySubentity(): ?string
     {
@@ -120,7 +120,7 @@ public function getCountrySubentity(): ?string
     }
 
     /**
-     * @param string $subentity
+     * @param string|null $countrySubentity
      * @return static
      */
     public function setCountrySubentity(?string $countrySubentity)
@@ -130,7 +130,7 @@ public function setCountrySubentity(?string $countrySubentity)
     }
 
     /**
-     * @return Country
+     * @return Country|null
      */
     public function getCountry(): ?Country
     {
@@ -138,7 +138,7 @@ public function getCountry(): ?Country
     }
 
     /**
-     * @param Country $country
+     * @param Country|null $country
      * @return static
      */
     public function setCountry(?Country $country)
@@ -179,7 +179,7 @@ public function addAddressLine(AddressLine $addressLine)
      * The xmlSerialize method is called during xml writing.
      *
      * @param Writer $writer
-     * @return static
+     * @return void
      */
     public function xmlSerialize(Writer $writer): void
     {
diff --git a/src/AddressLine.php b/src/AddressLine.php
index f9d2dfc..fcc861c 100644
--- a/src/AddressLine.php
+++ b/src/AddressLine.php
@@ -11,7 +11,7 @@
 
 class AddressLine implements XmlSerializable, XmlDeserializable
 {
-    private $line;
+    private ?string $line = null;
 
     /**
      * @return string|null
diff --git a/src/AllowanceCharge.php b/src/AllowanceCharge.php
index f379e51..9f3853c 100644
--- a/src/AllowanceCharge.php
+++ b/src/AllowanceCharge.php
@@ -12,13 +12,13 @@
 
 class AllowanceCharge implements XmlSerializable, XmlDeserializable
 {
-    private $chargeIndicator;
+    private bool $chargeIndicator;
     private $allowanceChargeReasonCode;
-    private $allowanceChargeReason;
-    private $multiplierFactorNumeric;
-    private $baseAmount;
-    private $amount;
-    private $taxCategory;
+    private ?string $allowanceChargeReason = null;
+    private ?float $multiplierFactorNumeric = null;
+    private ?float $baseAmount = null;
+    private ?float $amount = null;
+    private ?TaxCategory $taxCategory = null;
 
     /**
      * @return bool
@@ -57,7 +57,7 @@ public function setAllowanceChargeReasonCode($allowanceChargeReasonCode)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getAllowanceChargeReason(): ?string
     {
@@ -65,7 +65,7 @@ public function getAllowanceChargeReason(): ?string
     }
 
     /**
-     * @param string $allowanceChargeReason
+     * @param string|null $allowanceChargeReason
      * @return static
      */
     public function setAllowanceChargeReason(?string $allowanceChargeReason)
@@ -75,7 +75,7 @@ public function setAllowanceChargeReason(?string $allowanceChargeReason)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getMultiplierFactorNumeric(): ?float
     {
@@ -83,7 +83,7 @@ public function getMultiplierFactorNumeric(): ?float
     }
 
     /**
-     * @param float $multiplierFactorNumeric
+     * @param float|null $multiplierFactorNumeric
      * @return static
      */
     public function setMultiplierFactorNumeric(?float $multiplierFactorNumeric)
@@ -93,7 +93,7 @@ public function setMultiplierFactorNumeric(?float $multiplierFactorNumeric)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getBaseAmount(): ?float
     {
@@ -101,7 +101,7 @@ public function getBaseAmount(): ?float
     }
 
     /**
-     * @param float $baseAmount
+     * @param float|null $baseAmount
      * @return static
      */
     public function setBaseAmount(?float $baseAmount)
@@ -111,7 +111,7 @@ public function setBaseAmount(?float $baseAmount)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getAmount(): ?float
     {
@@ -119,7 +119,7 @@ public function getAmount(): ?float
     }
 
     /**
-     * @param float $amount
+     * @param float|null $amount
      * @return static
      */
     public function setAmount(?float $amount)
@@ -129,7 +129,7 @@ public function setAmount(?float $amount)
     }
 
     /**
-     * @return TaxCategory
+     * @return TaxCategory|null
      */
     public function getTaxCategory(): ?TaxCategory
     {
@@ -137,7 +137,7 @@ public function getTaxCategory(): ?TaxCategory
     }
 
     /**
-     * @param TaxCategory $taxCategory
+     * @param TaxCategory|null $taxCategory
      * @return static
      */
     public function setTaxCategory(?TaxCategory $taxCategory)
@@ -225,7 +225,7 @@ private static function parseAllowanceChargeReasonCode(?string $value)
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -233,13 +233,33 @@ public static function xmlDeserialize(Reader $reader)
         $mixedContent = mixedContent($reader);
         $collection = new ArrayCollection($mixedContent);
 
+        $allowanceChargeReasonCode = self::parseAllowanceChargeReasonCode(
+            ReaderHelper::getTagValue(Schema::CBC . 'AllowanceChargeReasonCode', $collection)
+        );
+
+        $multiplierFactorNumericTagValue = ReaderHelper::getTagValue(
+            Schema::CBC . 'MultiplierFactorNumeric',
+            $collection
+        );
+        $multiplierFactorNumeric = $multiplierFactorNumericTagValue !== null
+            ? floatval(ReaderHelper::getTagValue(Schema::CBC . 'MultiplierFactorNumeric', $collection))
+            : null;
+
+        $baseAmount = ReaderHelper::getTagValue(Schema::CBC . 'BaseAmount', $collection) !== null
+            ? floatval(ReaderHelper::getTagValue(Schema::CBC . 'BaseAmount', $collection))
+            : null;
+
+        $amount = ReaderHelper::getTagValue(Schema::CBC . 'Amount', $collection) !== null
+            ? floatval(ReaderHelper::getTagValue(Schema::CBC . 'Amount', $collection))
+            : null;
+
         return (new static())
             ->setChargeIndicator(ReaderHelper::getTagValue(Schema::CBC . 'ChargeIndicator', $collection) === 'true')
-            ->setAllowanceChargeReasonCode(self::parseAllowanceChargeReasonCode(ReaderHelper::getTagValue(Schema::CBC . 'AllowanceChargeReasonCode', $collection)))
+            ->setAllowanceChargeReasonCode($allowanceChargeReasonCode)
             ->setAllowanceChargeReason(ReaderHelper::getTagValue(Schema::CBC . 'AllowanceChargeReason', $collection))
-            ->setMultiplierFactorNumeric(ReaderHelper::getTagValue(Schema::CBC . 'MultiplierFactorNumeric', $collection) !== null ? floatval(ReaderHelper::getTagValue(Schema::CBC . 'MultiplierFactorNumeric', $collection)) : null)
-            ->setBaseAmount(ReaderHelper::getTagValue(Schema::CBC . 'BaseAmount', $collection) !== null ? floatval(ReaderHelper::getTagValue(Schema::CBC . 'BaseAmount', $collection)) : null)
-            ->setAmount(ReaderHelper::getTagValue(Schema::CBC . 'Amount', $collection) !== null ? floatval(ReaderHelper::getTagValue(Schema::CBC . 'Amount', $collection)) : null)
+            ->setMultiplierFactorNumeric($multiplierFactorNumeric)
+            ->setBaseAmount($baseAmount)
+            ->setAmount($amount)
             ->setTaxCategory(ReaderHelper::getTagValue(Schema::CAC . 'TaxCategory', $collection));
     }
 }
diff --git a/src/Attachment.php b/src/Attachment.php
index 4203dde..4d0e5ab 100644
--- a/src/Attachment.php
+++ b/src/Attachment.php
@@ -15,15 +15,15 @@
 
 class Attachment implements XmlSerializable, XmlDeserializable
 {
-    private $filePath;
-    private $externalReference;
-    private $base64Content;
-    private $fileName;
-    private $mimeType;
+    private ?string $filePath = null;
+    private ?string $externalReference = null;
+    private ?string $base64Content = null;
+    private ?string $fileName = null;
+    private ?string $mimeType = null;
 
     /**
-     * @throws Exception exception when the mime type cannot be determined
      * @return string
+     * @throws Exception exception when the mime type cannot be determined
      */
     public function getFilePathMimeType(): string
     {
@@ -35,7 +35,7 @@ public function getFilePathMimeType(): string
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getFilePath(): ?string
     {
@@ -53,7 +53,7 @@ public function setFilePath(string $filePath)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getExternalReference(): ?string
     {
@@ -70,6 +70,9 @@ public function setExternalReference(string $externalReference)
         return $this;
     }
 
+    /**
+     * @return string|null
+     */
     public function getBase64Content(): ?string
     {
         return $this->base64Content;
@@ -91,7 +94,7 @@ public function setBase64Content(string $base64Content, ?string $fileName, ?stri
     }
 
     /**
-     * @return ?string
+     * @return string|null
      */
     public function getFileName(): ?string
     {
@@ -109,7 +112,7 @@ public function setFileName(?string $fileName)
     }
 
     /**
-     * @return ?string
+     * @return string|null
      */
     public function getMimeType(): ?string
     {
@@ -129,17 +132,19 @@ public function setMimeType(?string $mimeType)
     /**
      * The validate function that is called during xml writing to valid the data of the object.
      *
-     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      * @return void
+     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      */
     public function validate()
     {
         if ($this->filePath === null && $this->externalReference === null && $this->base64Content === null) {
-            throw new InvalidArgumentException('Attachment must have a filePath, an externalReference, or a fileContent');
+            $message = 'Attachment must have a filePath, an externalReference, or a fileContent';
+            throw new InvalidArgumentException($message);
         }
 
         if ($this->base64Content !== null && $this->mimeType === null) {
-            throw new InvalidArgumentException('Using base64Content, you need to define a mimeType by also using setFileMimeType');
+            $message = 'Using base64Content, you need to define a mimeType by also using setFileMimeType';
+            throw new InvalidArgumentException($message);
         }
 
         if ($this->filePath !== null && !file_exists($this->filePath)) {
@@ -152,6 +157,7 @@ public function validate()
      *
      * @param Writer $writer
      * @return void
+     * @throws Exception
      */
     public function xmlSerialize(Writer $writer): void
     {
@@ -188,7 +194,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
diff --git a/src/BillingReference.php b/src/BillingReference.php
index bb28820..195dbe0 100644
--- a/src/BillingReference.php
+++ b/src/BillingReference.php
@@ -13,11 +13,11 @@
 
 class BillingReference implements XmlSerializable, XmlDeserializable
 {
-    private $invoiceDocumentReference;
+    private ?InvoiceDocumentReference $invoiceDocumentReference = null;
 
     /**
      *
-     * @return ?InvoiceDocumentReference
+     * @return InvoiceDocumentReference|null
      */
     public function getInvoiceDocumentReference(): ?InvoiceDocumentReference
     {
@@ -37,8 +37,8 @@ public function setInvoiceDocumentReference($invoiceDocumentReference)
     /**
      * The validate function that is called during xml writing to valid the data of the object.
      *
-     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      * @return void
+     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      */
     public function validate()
     {
@@ -61,7 +61,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -69,7 +69,6 @@ public static function xmlDeserialize(Reader $reader)
         $keyValues = keyValue($reader);
 
         return (new static())
-            ->setInvoiceDocumentReference($keyValues[Schema::CAC . 'InvoiceDocumentReference'] ?? null)
-        ;
+            ->setInvoiceDocumentReference($keyValues[Schema::CAC . 'InvoiceDocumentReference'] ?? null);
     }
 }
diff --git a/src/ClassifiedTaxCategory.php b/src/ClassifiedTaxCategory.php
index bac69cc..40b5108 100644
--- a/src/ClassifiedTaxCategory.php
+++ b/src/ClassifiedTaxCategory.php
@@ -14,17 +14,17 @@
 
 class ClassifiedTaxCategory implements XmlSerializable, XmlDeserializable
 {
-    private $id;
-    private $name;
-    private $percent;
-    private $taxScheme;
-    private $taxExemptionReason;
-    private $taxExemptionReasonCode;
-    private $schemeID;
-    private $schemeName;
+    private ?string $id = null;
+    private ?string $name = null;
+    private ?float $percent = null;
+    private ?TaxScheme $taxScheme = null;
+    private ?string $taxExemptionReason = null;
+    private ?string $taxExemptionReasonCode = null;
+    private ?string $schemeID = null;
+    private ?string $schemeName = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getId(): ?string
     {
@@ -42,7 +42,7 @@ public function getId(): ?string
     }
 
     /**
-     * @param string $id
+     * @param string|null $id
      * @return static
      */
     public function setId(?string $id)
@@ -52,7 +52,7 @@ public function setId(?string $id)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getName(): ?string
     {
@@ -60,7 +60,7 @@ public function getName(): ?string
     }
 
     /**
-     * @param string $name
+     * @param string|null $name
      * @return static
      */
     public function setName(?string $name)
@@ -70,7 +70,7 @@ public function setName(?string $name)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getPercent(): ?float
     {
@@ -78,7 +78,7 @@ public function getPercent(): ?float
     }
 
     /**
-     * @param float $percent
+     * @param float|null $percent
      * @return static
      */
     public function setPercent(?float $percent)
@@ -88,7 +88,7 @@ public function setPercent(?float $percent)
     }
 
     /**
-     * @return TaxScheme
+     * @return TaxScheme|null
      */
     public function getTaxScheme(): ?TaxScheme
     {
@@ -96,7 +96,7 @@ public function getTaxScheme(): ?TaxScheme
     }
 
     /**
-     * @param TaxScheme $taxScheme
+     * @param TaxScheme|null $taxScheme
      * @return static
      */
     public function setTaxScheme(?TaxScheme $taxScheme)
@@ -106,7 +106,7 @@ public function setTaxScheme(?TaxScheme $taxScheme)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getSchemeId(): ?string
     {
@@ -114,7 +114,7 @@ public function getSchemeId(): ?string
     }
 
     /**
-     * @param string $id
+     * @param string|null $id
      * @return static
      */
     public function setSchemeId(?string $id)
@@ -124,7 +124,7 @@ public function setSchemeId(?string $id)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getSchemeName(): ?string
     {
@@ -132,7 +132,7 @@ public function getSchemeName(): ?string
     }
 
     /**
-     * @param string $name
+     * @param string|null $name
      * @return static
      */
     public function setSchemeName(?string $name)
@@ -142,7 +142,7 @@ public function setSchemeName(?string $name)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getTaxExemptionReason(): ?string
     {
@@ -150,7 +150,7 @@ public function getTaxExemptionReason(): ?string
     }
 
     /**
-     * @param string $taxExemptionReason
+     * @param string|null $taxExemptionReason
      * @return static
      */
     public function setTaxExemptionReason(?string $taxExemptionReason)
@@ -160,7 +160,7 @@ public function setTaxExemptionReason(?string $taxExemptionReason)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getTaxExemptionReasonCode(): ?string
     {
@@ -168,7 +168,7 @@ public function getTaxExemptionReasonCode(): ?string
     }
 
     /**
-     * @param string $taxExemptionReasonCode
+     * @param string|null $taxExemptionReasonCode
      * @return static
      */
     public function setTaxExemptionReasonCode(?string $taxExemptionReasonCode)
@@ -180,8 +180,8 @@ public function setTaxExemptionReasonCode(?string $taxExemptionReasonCode)
     /**
      * The validate function that is called during xml writing to valid the data of the object.
      *
-     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      * @return void
+     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      */
     public function validate()
     {
@@ -247,7 +247,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -270,7 +270,6 @@ public static function xmlDeserialize(Reader $reader)
             ->setTaxExemptionReason($taxExemptionReasonTag['value'] ?? null)
             ->setTaxExemptionReasonCode($taxExemptionReasonCodeTag['value'] ?? null)
             ->setSchemeId($idTag['attributes']['schemeID'] ?? null)
-            ->setSchemeName($idTag['attributes']['schemeName'] ?? null)
-        ;
+            ->setSchemeName($idTag['attributes']['schemeName'] ?? null);
     }
 }
diff --git a/src/CommodityClassification.php b/src/CommodityClassification.php
index a57a8b9..f5dc5fa 100644
--- a/src/CommodityClassification.php
+++ b/src/CommodityClassification.php
@@ -12,12 +12,12 @@
 
 class CommodityClassification implements XmlSerializable, XmlDeserializable
 {
-    private $itemClassificationCode = null;
-    private $itemClassificationListId = null;
-    private $itemClassificationListVersionId = null;
+    private ?string $itemClassificationCode = null;
+    private ?string $itemClassificationListId = null;
+    private ?string $itemClassificationListVersionId = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getItemClassificationCode(): ?string
     {
@@ -25,7 +25,7 @@ public function getItemClassificationCode(): ?string
     }
 
     /**
-     * @param string $itemClassificationCode
+     * @param string|null $itemClassificationCode
      * @return static
      */
     public function setItemClassificationCode(?string $itemClassificationCode)
@@ -35,7 +35,7 @@ public function setItemClassificationCode(?string $itemClassificationCode)
     }
 
     /**
-     * @return ?string
+     * @return string|null
      */
     public function getItemClassificationListId(): ?string
     {
@@ -53,7 +53,7 @@ public function setItemClassificationListId(?string $itemClassificationListId)
     }
 
     /**
-     * @return ?string
+     * @return string|null
      */
     public function getItemClassificationListVersionId(): ?string
     {
@@ -97,14 +97,14 @@ public function xmlSerialize(Writer $writer): void
      * The xmlDeserialize method is called during xml reading.
      *
      * @param Reader $reader
-     * @return void
+     * @return CommodityClassification
      */
     public static function xmlDeserialize(Reader $reader)
     {
         $mixedContent = mixedContent($reader);
         $collection = new ArrayCollection($mixedContent);
 
-        // UBL CommodityClassification kan zowel ItemClassificationCode als CommodityCode bevatten
+        // UBL CommodityClassification can contain both ItemClassificationCode and CommodityCode
         $classificationCode = ReaderHelper::getTag(Schema::CBC . 'ItemClassificationCode', $collection)
             ?? ReaderHelper::getTag(Schema::CBC . 'CommodityCode', $collection);
 
diff --git a/src/Contact.php b/src/Contact.php
index e3c9a8f..f2e4e8a 100644
--- a/src/Contact.php
+++ b/src/Contact.php
@@ -11,14 +11,14 @@
 
 class Contact implements XmlSerializable, XmlDeserializable
 {
-    private $id;
-    private $name;
-    private $telephone;
-    private $telefax;
-    private $electronicMail;
+    private ?string $id = null;
+    private ?string $name = null;
+    private ?string $telephone = null;
+    private ?string $telefax = null;
+    private ?string $electronicMail = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getId(): ?string
     {
@@ -36,7 +36,7 @@ public function setId(string $id): Contact
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getName(): ?string
     {
@@ -54,7 +54,7 @@ public function setName($name)
     }
 
     /**
-     * @return mixed
+     * @return string|null
      */
     public function getTelephone(): ?string
     {
@@ -62,7 +62,7 @@ public function getTelephone(): ?string
     }
 
     /**
-     * @param string $telephone
+     * @param string|null $telephone
      * @return static
      */
     public function setTelephone(?string $telephone)
@@ -72,7 +72,7 @@ public function setTelephone(?string $telephone)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getTelefax(): ?string
     {
@@ -80,7 +80,7 @@ public function getTelefax(): ?string
     }
 
     /**
-     * @param string $telefax
+     * @param string|null $telefax
      * @return static
      */
     public function setTelefax(?string $telefax)
@@ -90,7 +90,7 @@ public function setTelefax(?string $telefax)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getElectronicMail(): ?string
     {
@@ -98,7 +98,7 @@ public function getElectronicMail(): ?string
     }
 
     /**
-     * @param string $electronicMail
+     * @param string|null $electronicMail
      * @return static
      */
     public function setElectronicMail(?string $electronicMail)
@@ -148,7 +148,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -160,6 +160,5 @@ public static function xmlDeserialize(Reader $reader)
             ->setTelephone($keyValues[Schema::CBC . 'Telephone'] ?? null)
             ->setTelefax($keyValues[Schema::CBC . 'Telefax'] ?? null)
             ->setElectronicMail($keyValues[Schema::CBC . 'ElectronicMail'] ?? null);
-        ;
     }
 }
diff --git a/src/ContractDocumentReference.php b/src/ContractDocumentReference.php
index 44de036..c80bccf 100644
--- a/src/ContractDocumentReference.php
+++ b/src/ContractDocumentReference.php
@@ -11,7 +11,7 @@
 
 class ContractDocumentReference implements XmlSerializable, XmlDeserializable
 {
-    private $id;
+    private ?string $id = null;
 
     /**
      * @return string|null
@@ -46,7 +46,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -54,7 +54,6 @@ public static function xmlDeserialize(Reader $reader)
         $mixedContent = keyValue($reader);
 
         return (new static())
-            ->setId($mixedContent[Schema::CBC . 'ID'] ?? null)
-        ;
+            ->setId($mixedContent[Schema::CBC . 'ID'] ?? null);
     }
 }
diff --git a/src/Country.php b/src/Country.php
index e9a8315..0a75a7b 100644
--- a/src/Country.php
+++ b/src/Country.php
@@ -15,7 +15,7 @@ class Country implements XmlSerializable, XmlDeserializable
     private $listId;
 
     /**
-     * @return mixed
+     * @return string|null
      */
     public function getIdentificationCode(): ?string
     {
@@ -33,7 +33,7 @@ public function setIdentificationCode(?string $identificationCode)
     }
 
     /**
-     * @return mixed
+     * @return string|null
      */
     public function getListId(): ?string
     {
@@ -41,7 +41,7 @@ public function getListId(): ?string
     }
 
     /**
-     * @param mixed $listId
+     * @param string|null $listId
      * @return static
      */
     public function setListId(?string $listId)
@@ -73,7 +73,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -82,7 +82,6 @@ public static function xmlDeserialize(Reader $reader)
 
         return (new static())
             ->setIdentificationCode($keyValues[Schema::CBC . 'IdentificationCode'])
-            ->setListId($keyValues[Schema::CBC . 'IdentificationCode']['attributes']['listID'] ?? null)
-        ;
+            ->setListId($keyValues[Schema::CBC . 'IdentificationCode']['attributes']['listID'] ?? null);
     }
 }
diff --git a/src/CreditNote.php b/src/CreditNote.php
index 90e3bb2..0c65b46 100644
--- a/src/CreditNote.php
+++ b/src/CreditNote.php
@@ -11,11 +11,11 @@
 
 class CreditNote extends Invoice implements XmlSerializable, XmlDeserializable
 {
-    public $xmlTagName = 'CreditNote';
-    protected $invoiceTypeCode = InvoiceTypeCode::CREDIT_NOTE;
+    public string $xmlTagName = 'CreditNote';
+    protected ?int $invoiceTypeCode = InvoiceTypeCode::CREDIT_NOTE;
 
     /**
-     * @return CreditNoteLine[]
+     * @return CreditNoteLine[]|null
      */
     public function getCreditNoteLines(): ?array
     {
diff --git a/src/CreditNoteLine.php b/src/CreditNoteLine.php
index 3f33ee5..9adbdd1 100644
--- a/src/CreditNoteLine.php
+++ b/src/CreditNoteLine.php
@@ -9,10 +9,10 @@
 
 class CreditNoteLine extends InvoiceLine
 {
-    public $xmlTagName = 'CreditNoteLine';
+    public string $xmlTagName = 'CreditNoteLine';
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getCreditedQuantity(): ?float
     {
@@ -31,7 +31,7 @@ public function setCreditedQuantity(?float $creditedQuantity)
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
diff --git a/src/DebitNote.php b/src/DebitNote.php
index 0c93a5d..41280ea 100644
--- a/src/DebitNote.php
+++ b/src/DebitNote.php
@@ -11,11 +11,11 @@
 
 class DebitNote extends Invoice implements XmlSerializable, XmlDeserializable
 {
-    public $xmlTagName = 'DebitNote';
-    protected $invoiceTypeCode = InvoiceTypeCode::DEBIT_NOTE;
+    public string $xmlTagName = 'DebitNote';
+    protected ?int $invoiceTypeCode = InvoiceTypeCode::DEBIT_NOTE;
 
     /**
-     * @return DebitNoteLine[]
+     * @return DebitNoteLine[]|null
      */
     public function getDebitNoteLines(): ?array
     {
diff --git a/src/DebitNoteLine.php b/src/DebitNoteLine.php
index e9fdf70..79c4fe0 100644
--- a/src/DebitNoteLine.php
+++ b/src/DebitNoteLine.php
@@ -9,10 +9,10 @@
 
 class DebitNoteLine extends InvoiceLine
 {
-    public $xmlTagName = 'DebitNoteLine';
+    public string $xmlTagName = 'DebitNoteLine';
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getDebitedQuantity(): ?float
     {
@@ -31,7 +31,7 @@ public function setDebitedQuantity(?float $debitedQuantity)
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
diff --git a/src/Delivery.php b/src/Delivery.php
index e944cab..1415b11 100644
--- a/src/Delivery.php
+++ b/src/Delivery.php
@@ -14,12 +14,12 @@
 
 class Delivery implements XmlSerializable, XmlDeserializable
 {
-    private $actualDeliveryDate;
-    private $deliveryLocation;
-    private $deliveryParty;
+    private ?DateTime $actualDeliveryDate = null;
+    private ?Address $deliveryLocation = null;
+    private ?Party $deliveryParty = null;
 
     /**
-     * @return DateTime
+     * @return DateTime|null
      */
     public function getActualDeliveryDate(): ?DateTime
     {
@@ -27,7 +27,7 @@ public function getActualDeliveryDate(): ?DateTime
     }
 
     /**
-     * @param DateTime $actualDeliveryDate
+     * @param DateTime|null $actualDeliveryDate
      * @return static
      */
     public function setActualDeliveryDate(?DateTime $actualDeliveryDate)
@@ -37,7 +37,7 @@ public function setActualDeliveryDate(?DateTime $actualDeliveryDate)
     }
 
     /**
-     * @return Address
+     * @return Address|null
      */
     public function getDeliveryLocation()
     {
@@ -45,17 +45,17 @@ public function getDeliveryLocation()
     }
 
     /**
-     * @param Address $deliveryLocation
+     * @param Address|null $deliveryLocation
      * @return static
      */
-    public function setDeliveryLocation($deliveryLocation)
+    public function setDeliveryLocation(?Address $deliveryLocation)
     {
         $this->deliveryLocation = $deliveryLocation;
         return $this;
     }
 
     /**
-     * @return Party
+     * @return Party|null
      */
     public function getDeliveryParty()
     {
@@ -63,10 +63,10 @@ public function getDeliveryParty()
     }
 
     /**
-     * @param Party $deliveryParty
+     * @param Party|null $deliveryParty
      * @return static
      */
-    public function setDeliveryParty($deliveryParty)
+    public function setDeliveryParty(?Party $deliveryParty)
     {
         $this->deliveryParty = $deliveryParty;
         return $this;
@@ -99,17 +99,20 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
     {
         $keyValues = keyValue($reader);
 
+        $actualDeliveryDate = isset($keyValues[Schema::CBC . 'ActualDeliveryDate'])
+            ? Carbon::parse($keyValues[Schema::CBC . 'ActualDeliveryDate'])->toDateTime()
+            : null;
+
         return (new static())
-            ->setActualDeliveryDate(isset($keyValues[Schema::CBC . 'ActualDeliveryDate']) ? Carbon::parse($keyValues[Schema::CBC . 'ActualDeliveryDate'])->toDateTime() : null)
+            ->setActualDeliveryDate($actualDeliveryDate)
             ->setDeliveryLocation($keyValues[Schema::CAC . 'DeliveryLocation'] ?? null)
-            ->setDeliveryParty($keyValues[Schema::CAC . 'DeliveryParty'] ?? null)
-        ;
+            ->setDeliveryParty($keyValues[Schema::CAC . 'DeliveryParty'] ?? null);
     }
 }
diff --git a/src/DespatchDocumentReference.php b/src/DespatchDocumentReference.php
index 96d84ed..63ab1a7 100644
--- a/src/DespatchDocumentReference.php
+++ b/src/DespatchDocumentReference.php
@@ -11,10 +11,10 @@
 
 class DespatchDocumentReference implements XmlSerializable, XmlDeserializable
 {
-    private $id;
+    private ?string $id = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getId(): ?string
     {
@@ -22,7 +22,7 @@ public function getId(): ?string
     }
 
     /**
-     * @param string $id
+     * @param string|null $id
      * @return static
      */
     public function setId(?string $id)
@@ -46,7 +46,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
diff --git a/src/FinancialInstitutionBranch.php b/src/FinancialInstitutionBranch.php
index 4fc27a8..ecadeb6 100644
--- a/src/FinancialInstitutionBranch.php
+++ b/src/FinancialInstitutionBranch.php
@@ -11,10 +11,10 @@
 
 class FinancialInstitutionBranch implements XmlSerializable, XmlDeserializable
 {
-    private $id;
+    private ?string $id = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getId(): ?string
     {
@@ -22,7 +22,7 @@ public function getId(): ?string
     }
 
     /**
-     * @param string $id
+     * @param string|null $id
      * @return static
      */
     public function setId(?string $id)
@@ -42,7 +42,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
diff --git a/src/Generator.php b/src/Generator.php
index cd589f7..4761c8c 100644
--- a/src/Generator.php
+++ b/src/Generator.php
@@ -6,9 +6,9 @@
 
 class Generator
 {
-    public static $currencyID;
+    public static string $currencyID;
 
-    public static function invoice(Invoice $invoice, $currencyId = 'EUR')
+    public static function invoice(Invoice $invoice, string $currencyId = 'EUR')
     {
         self::$currencyID = $currencyId;
 
@@ -25,7 +25,7 @@ public static function invoice(Invoice $invoice, $currencyId = 'EUR')
         ]);
     }
 
-    public static function creditNote(CreditNote $creditNote, $currencyId = 'EUR')
+    public static function creditNote(CreditNote $creditNote, string $currencyId = 'EUR')
     {
         self::$currencyID = $currencyId;
 
diff --git a/src/Invoice.php b/src/Invoice.php
index c4aede7..2e0d36e 100644
--- a/src/Invoice.php
+++ b/src/Invoice.php
@@ -14,47 +14,47 @@
 use function Sabre\Xml\Deserializer\mixedContent;
 class Invoice implements XmlSerializable, XmlDeserializable
 {
-    public $xmlTagName = "Invoice";
-    private $UBLVersionID = "2.1";
-    private $customizationID = "1.0";
-    private $profileID;
-    private $id;
-    private $copyIndicator;
-    private $issueDate;
-    private ?DateTime $issueTime;
-    protected $invoiceTypeCode = InvoiceTypeCode::INVOICE;
-    private $note;
-    private $taxPointDate;
-    private $dueDate;
-    private $paymentTerms;
-    private $accountingSupplierParty;
-    private $accountingCustomerParty;
-    private $accountingCustomerPartyContact;
-    private $payeeParty;
+    public string $xmlTagName = "Invoice";
+    private ?string $UBLVersionID = "2.1";
+    private ?string $customizationID = "1.0";
+    private ?string $profileID = null;
+    private ?string $id = null;
+    private ?bool $copyIndicator = null;
+    private ?DateTime $issueDate = null;
+    private ?DateTime $issueTime = null;
+    protected ?int $invoiceTypeCode = InvoiceTypeCode::INVOICE;
+    private ?string $note = null;
+    private ?DateTime $taxPointDate = null;
+    private ?DateTime $dueDate = null;
+    private ?PaymentTerms $paymentTerms = null;
+    private ?AccountingParty $accountingSupplierParty = null;
+    private ?AccountingParty $accountingCustomerParty = null;
+    private ?Contact $accountingCustomerPartyContact = null;
+    private ?PayeeParty $payeeParty = null;
     /** @var PaymentMeans[] $paymentMeans */
-    private $paymentMeans;
-    private $taxTotal;
-    private $legalMonetaryTotal;
+    private ?array $paymentMeans = null;
+    private ?TaxTotal $taxTotal = null;
+    private ?LegalMonetaryTotal $legalMonetaryTotal = null;
     /** @var InvoiceLine[] $invoiceLines */
-    protected $invoiceLines;
-    private $allowanceCharges;
-    private $additionalDocumentReferences = [];
-    private $projectReference;
-    private $documentCurrencyCode = "EUR";
-    private $taxCurrencyCode;
-    private $buyerReference;
-    private $accountingCostCode;
-    private $invoicePeriod;
-    private $billingReference;
-    private $delivery;
-    private $orderReference;
-    private $contractDocumentReference;
-    private $despatchDocumentReference;
-    private $receiptDocumentReference;
-    private $originatorDocumentReference;
-
-    /**
-     * @return string
+    protected array $invoiceLines = [];
+    private ?array $allowanceCharges = null;
+    private array $additionalDocumentReferences = [];
+    private ?ProjectReference $projectReference = null;
+    private ?string $documentCurrencyCode = "EUR";
+    private ?string $taxCurrencyCode = null;
+    private ?string $buyerReference = null;
+    private ?string $accountingCostCode = null;
+    private ?InvoicePeriod $invoicePeriod = null;
+    private ?BillingReference $billingReference = null;
+    private ?Delivery $delivery = null;
+    private ?OrderReference $orderReference = null;
+    private ?ContractDocumentReference $contractDocumentReference = null;
+    private ?DespatchDocumentReference $despatchDocumentReference = null;
+    private ?ReceiptDocumentReference $receiptDocumentReference = null;
+    private ?OriginatorDocumentReference $originatorDocumentReference = null;
+
+    /**
+     * @return string|null
      */
     public function getUBLVersionId(): ?string
     {
@@ -62,7 +62,7 @@ public function getUBLVersionId(): ?string
     }
 
     /**
-     * @param string $UBLVersionID
+     * @param string|null $UBLVersionID
      *                             eg. '2.0', '2.1', '2.2', ...
      * @return static
      */
@@ -73,7 +73,7 @@ public function setUBLVersionId(?string $UBLVersionID)
     }
 
     /**
-     * @return mixed
+     * @return string|null
      */
     public function getId(): ?string
     {
@@ -81,7 +81,7 @@ public function getId(): ?string
     }
 
     /**
-     * @param mixed $id
+     * @param string|null $id
      * @return static
      */
     public function setId(?string $id)
@@ -99,7 +99,7 @@ public function getCustomizationId(): ?string
     }
 
     /**
-     * @param mixed $customizationID
+     * @param string|null $customizationID
      * @return static
      */
     public function setCustomizationId(?string $customizationID)
@@ -145,7 +145,7 @@ public function setCopyIndicator(bool $copyIndicator)
     }
 
     /**
-     * @return DateTime
+     * @return DateTime|null
      */
     public function getIssueDate(): ?DateTime
     {
@@ -153,7 +153,7 @@ public function getIssueDate(): ?DateTime
     }
 
     /**
-     * @param DateTime $issueDate
+     * @param DateTime|null $issueDate
      * @return static
      */
     public function setIssueDate(?DateTime $issueDate)
@@ -171,7 +171,7 @@ public function getIssueTime() : ?DateTime
     }
 
     /**
-     * @param DateTime $issueTime
+     * @param DateTime|null $issueTime
      * @return static
      */
     public function setIssueTime(?DateTime $issueTime = null) : self
@@ -182,7 +182,7 @@ public function setIssueTime(?DateTime $issueTime = null) : self
     }
 
     /**
-     * @return DateTime
+     * @return DateTime|null
      */
     public function getDueDate(): ?DateTime
     {
@@ -200,7 +200,7 @@ public function setDueDate(?DateTime $dueDate)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getDocumentCurrencyCode(): ?string
     {
@@ -208,7 +208,7 @@ public function getDocumentCurrencyCode(): ?string
     }
 
     /**
-     * @param mixed $currencyCode
+     * @param string|null $currencyCode
      * @return static
      */
     public function setDocumentCurrencyCode(?string $currencyCode = "EUR")
@@ -218,7 +218,7 @@ public function setDocumentCurrencyCode(?string $currencyCode = "EUR")
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getTaxCurrencyCode(): ?string
     {
@@ -236,7 +236,7 @@ public function setTaxCurrencyCode(?string $currencyCode)
     }
 
     /**
-     * @return int
+     * @return int|null
      */
     public function getInvoiceTypeCode(): ?int
     {
@@ -244,7 +244,7 @@ public function getInvoiceTypeCode(): ?int
     }
 
     /**
-     * @param int $invoiceTypeCode
+     * @param int|null $invoiceTypeCode
      *                             See also: src/InvoiceTypeCode.php
      * @return static
      */
@@ -255,7 +255,7 @@ public function setInvoiceTypeCode(?int $invoiceTypeCode)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getNote()
     {
@@ -263,7 +263,7 @@ public function getNote()
     }
 
     /**
-     * @param ?string $note
+     * @param string|null $note
      * @return static
      */
     public function setNote(?string $note)
@@ -273,7 +273,7 @@ public function setNote(?string $note)
     }
 
     /**
-     * @return DateTime
+     * @return DateTime|null
      */
     public function getTaxPointDate(): ?DateTime
     {
@@ -291,7 +291,7 @@ public function setTaxPointDate(?DateTime $taxPointDate)
     }
 
     /**
-     * @return PaymentTerms
+     * @return PaymentTerms|null
      */
     public function getPaymentTerms(): ?PaymentTerms
     {
@@ -309,7 +309,7 @@ public function setPaymentTerms(?PaymentTerms $paymentTerms)
     }
 
     /**
-     * @return AccountingParty
+     * @return AccountingParty|null
      */
     public function getAccountingSupplierParty(): ?AccountingParty
     {
@@ -328,7 +328,7 @@ public function setAccountingSupplierParty(
     }
 
     /**
-     * @return AccountingParty
+     * @return AccountingParty|null
      */
     public function getAccountingCustomerParty(): ?AccountingParty
     {
@@ -347,7 +347,7 @@ public function setAccountingCustomerParty(
     }
 
     /**
-     * @return ?Contact
+     * @return Contact|null
      */
     public function getAccountingCustomerPartyContact(): ?Contact
     {
@@ -366,7 +366,7 @@ public function setAccountingCustomerPartyContact(
     }
 
     /**
-     * @return PayeeParty
+     * @return PayeeParty|null
      */
     public function getPayeeParty(): ?PayeeParty
     {
@@ -374,7 +374,7 @@ public function getPayeeParty(): ?PayeeParty
     }
 
     /**
-     * @param PayeeParty $payeeParty
+     * @param PayeeParty|null $payeeParty
      * @return static
      */
     public function setPayeeParty(?PayeeParty $payeeParty)
@@ -384,7 +384,7 @@ public function setPayeeParty(?PayeeParty $payeeParty)
     }
 
     /**
-     * @return PaymentMeans[]
+     * @return PaymentMeans[]|null
      */
     public function getPaymentMeans(): ?array
     {
@@ -392,17 +392,17 @@ public function getPaymentMeans(): ?array
     }
 
     /**
-     * @param PaymentMeans[] $paymentMeans
+     * @param PaymentMeans[]|null $paymentMeans
      * @return static
      */
-    public function setPaymentMeans(array $paymentMeans)
+    public function setPaymentMeans(?array $paymentMeans)
     {
         $this->paymentMeans = $paymentMeans;
         return $this;
     }
 
     /**
-     * @return TaxTotal
+     * @return TaxTotal|null
      */
     public function getTaxTotal(): ?TaxTotal
     {
@@ -420,7 +420,7 @@ public function setTaxTotal(TaxTotal $taxTotal)
     }
 
     /**
-     * @return LegalMonetaryTotal
+     * @return LegalMonetaryTotal|null
      */
     public function getLegalMonetaryTotal(): ?LegalMonetaryTotal
     {
@@ -439,7 +439,7 @@ public function setLegalMonetaryTotal(
     }
 
     /**
-     * @return staticLine[]
+     * @return InvoiceLine[]|null
      */
     public function getInvoiceLines(): ?array
     {
@@ -457,7 +457,7 @@ public function setInvoiceLines(array $invoiceLines)
     }
 
     /**
-     * @return AllowanceCharge[]
+     * @return AllowanceCharge[]|null
      */
     public function getAllowanceCharges(): ?array
     {
@@ -475,7 +475,7 @@ public function setAllowanceCharges(array $allowanceCharges)
     }
 
     /**
-     * @return AdditionalDocumentReference
+     * @return AdditionalDocumentReference|null
      * @deprecated Deprecated since v1.16 - Replace implementation with setAdditionalDocumentReference or addAdditionalDocumentReference to add/set a single AdditionalDocumentReference
      */
     public function getAdditionalDocumentReference(): ?AdditionalDocumentReference
@@ -503,7 +503,7 @@ public function setAdditionalDocumentReference(
     }
 
     /**
-     * @param AdditionalDocumentReference $additionalDocumentReference
+     * @param array $additionalDocumentReference
      * @return static
      */
     public function setAdditionalDocumentReferences(
@@ -536,7 +536,7 @@ public function setProjectReference(
     }
 
     /**
-     * @return ProjectReference projectReference
+     * @return ProjectReference|null
      */
     public function getProjectReference(): ?ProjectReference
     {
@@ -544,7 +544,7 @@ public function getProjectReference(): ?ProjectReference
     }
 
     /**
-     * @param string $buyerReference
+     * @param string|null $buyerReference
      * @return static
      */
     public function setBuyerReference(?string $buyerReference)
@@ -554,7 +554,7 @@ public function setBuyerReference(?string $buyerReference)
     }
 
     /**
-     * @return string buyerReference
+     * @return string|null
      */
     public function getBuyerReference(): ?string
     {
@@ -562,7 +562,7 @@ public function getBuyerReference(): ?string
     }
 
     /**
-     * @return mixed
+     * @return string|null
      */
     public function getAccountingCostCode(): ?string
     {
@@ -570,7 +570,7 @@ public function getAccountingCostCode(): ?string
     }
 
     /**
-     * @param mixed $accountingCostCode
+     * @param string|null $accountingCostCode
      * @return static
      */
     public function setAccountingCostCode(?string $accountingCostCode)
@@ -580,7 +580,7 @@ public function setAccountingCostCode(?string $accountingCostCode)
     }
 
     /**
-     * @return staticPeriod
+     * @return InvoicePeriod|null
      */
     public function getInvoicePeriod(): ?InvoicePeriod
     {
@@ -588,7 +588,7 @@ public function getInvoicePeriod(): ?InvoicePeriod
     }
 
     /**
-     * @param InvoicePeriod $invoicePeriod
+     * @param InvoicePeriod|null $invoicePeriod
      * @return static
      */
     public function setInvoicePeriod(?InvoicePeriod $invoicePeriod)
@@ -600,7 +600,7 @@ public function setInvoicePeriod(?InvoicePeriod $invoicePeriod)
     /**
      * Get the reference to the invoice that is being credited
      *
-     * @return ?BillingReference
+     * @return BillingReference|null
      */
     public function getBillingReference(): ?BillingReference
     {
@@ -619,7 +619,7 @@ public function setBillingReference(?BillingReference $billingReference)
     }
 
     /**
-     * @return Delivery
+     * @return Delivery|null
      */
     public function getDelivery(): ?Delivery
     {
@@ -627,7 +627,7 @@ public function getDelivery(): ?Delivery
     }
 
     /**
-     * @param Delivery $delivery
+     * @param Delivery|null $delivery
      * @return static
      */
     public function setDelivery(?Delivery $delivery)
@@ -637,7 +637,7 @@ public function setDelivery(?Delivery $delivery)
     }
 
     /**
-     * @return OrderReference
+     * @return OrderReference|null
      */
     public function getOrderReference(): ?OrderReference
     {
@@ -645,7 +645,7 @@ public function getOrderReference(): ?OrderReference
     }
 
     /**
-     * @param OrderReference $orderReference
+     * @param OrderReference|null $orderReference
      * @return static
      */
     public function setOrderReference(?OrderReference $orderReference)
@@ -655,7 +655,7 @@ public function setOrderReference(?OrderReference $orderReference)
     }
 
     /**
-     * @return ContractDocumentReference
+     * @return ContractDocumentReference|null
      */
     public function getContractDocumentReference(): ?ContractDocumentReference
     {
@@ -663,18 +663,17 @@ public function getContractDocumentReference(): ?ContractDocumentReference
     }
 
     /**
-     * @param ContractDocumentReference $ContractDocumentReference
+     * @param ContractDocumentReference|null $contractDocumentReference
      * @return static
      */
-    public function setContractDocumentReference(
-        ?ContractDocumentReference $contractDocumentReference
-    ) {
+    public function setContractDocumentReference(?ContractDocumentReference $contractDocumentReference)
+    {
         $this->contractDocumentReference = $contractDocumentReference;
         return $this;
     }
 
     /**
-     * @return DespatchDocumentReference
+     * @return DespatchDocumentReference|null
      */
     public function getDespatchDocumentReference(): ?DespatchDocumentReference
     {
@@ -682,7 +681,7 @@ public function getDespatchDocumentReference(): ?DespatchDocumentReference
     }
 
     /**
-     * @param DespatchDocumentReference $despatchDocumentReference
+     * @param DespatchDocumentReference|null $despatchDocumentReference
      * @return static
      */
     public function setDespatchDocumentReference(
@@ -693,7 +692,7 @@ public function setDespatchDocumentReference(
     }
 
     /**
-     * @return ReceiptDocumentReference
+     * @return ReceiptDocumentReference|null
      */
     public function getReceiptDocumentReference(): ?ReceiptDocumentReference
     {
@@ -701,7 +700,7 @@ public function getReceiptDocumentReference(): ?ReceiptDocumentReference
     }
 
     /**
-     * @param ReceiptDocumentReference $receiptDocumentReference
+     * @param ReceiptDocumentReference|null $receiptDocumentReference
      * @return static
      */
     public function setReceiptDocumentReference(
@@ -712,7 +711,7 @@ public function setReceiptDocumentReference(
     }
 
     /**
-     * @return OriginatorDocumentReference
+     * @return OriginatorDocumentReference|null
      */
     public function getOriginatorDocumentReference(): ?OriginatorDocumentReference
     {
@@ -720,7 +719,7 @@ public function getOriginatorDocumentReference(): ?OriginatorDocumentReference
     }
 
     /**
-     * @param OriginatorDocumentReference $originatorDocumentReference
+     * @param OriginatorDocumentReference|null $originatorDocumentReference
      * @return static
      */
     public function setOriginatorDocumentReference(
@@ -902,10 +901,7 @@ public function xmlSerialize(Writer $writer): void
         }
 
         if (!empty($this->additionalDocumentReferences)) {
-            foreach (
-                $this->additionalDocumentReferences
-                as $additionalDocumentReference
-            ) {
+            foreach ($this->additionalDocumentReferences as $additionalDocumentReference) {
                 $writer->write([
                     Schema::CAC .
                     "AdditionalDocumentReference" => $additionalDocumentReference,
@@ -988,7 +984,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
diff --git a/src/InvoiceDocumentReference.php b/src/InvoiceDocumentReference.php
index ffccb62..0592d8f 100644
--- a/src/InvoiceDocumentReference.php
+++ b/src/InvoiceDocumentReference.php
@@ -2,6 +2,7 @@
 
 namespace NumNum\UBL;
 
+use Exception;
 use function Sabre\Xml\Deserializer\keyValue;
 
 use DateTime;
@@ -13,12 +14,12 @@
 
 class InvoiceDocumentReference implements XmlSerializable, XmlDeserializable
 {
-    private $originalInvoiceId;
-    private $issueDate;
+    private ?string $originalInvoiceId = null;
+    private ?DateTime $issueDate = null;
 
     /**
      * Get the id of the invoice that is being credited
-     * @return string
+     * @return string|null
      */
     public function getOriginalInvoiceId(): ?string
     {
@@ -40,7 +41,7 @@ public function setOriginalInvoiceId(?string $invoiceRef)
     /**
      * Get the issue date of the original invoice that is being credited
      *
-     * @return ?DateTime
+     * @return DateTime|null
      */
     public function getIssueDate(): ?DateTime
     {
@@ -61,8 +62,8 @@ public function setIssueDate(?DateTime $issueDate)
     /**
      * The validate function that is called during xml writing to valid the data of the object.
      *
-     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      * @return void
+     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      */
     public function validate()
     {
@@ -99,16 +100,20 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
+     * @throws Exception
      */
     public static function xmlDeserialize(Reader $reader)
     {
         $mixedContent = keyValue($reader);
 
+        $issueDate = isset($mixedContent[Schema::CBC . 'IssueDate'])
+            ? new DateTime($mixedContent[Schema::CBC . 'IssueDate'])
+            : null;
+
         return (new static())
             ->setOriginalInvoiceId($mixedContent[Schema::CBC . 'ID'] ?? null)
-            ->setIssueDate(isset($mixedContent[Schema::CBC . 'IssueDate']) ? new DateTime($mixedContent[Schema::CBC . 'IssueDate']) : null)
-        ;
+            ->setIssueDate($issueDate);
     }
 }
diff --git a/src/InvoiceLine.php b/src/InvoiceLine.php
index acb5407..aad6509 100644
--- a/src/InvoiceLine.php
+++ b/src/InvoiceLine.php
@@ -12,22 +12,22 @@
 
 class InvoiceLine implements XmlSerializable, XmlDeserializable
 {
-    public $xmlTagName = 'InvoiceLine';
-    private $id;
-    protected $invoicedQuantity;
-    private $lineExtensionAmount;
-    private $unitCode = UnitCode::UNIT;
-    private $unitCodeListId;
-    private $taxTotal;
-    private $invoicePeriod;
-    private $orderLineReference;
-    private $note;
-    private $item;
-    private $price;
-    private $accountingCostCode;
-    private $accountingCost;
+    public string $xmlTagName = 'InvoiceLine';
+    private ?string $id = null;
+    protected ?float $invoicedQuantity = null;
+    private ?float $lineExtensionAmount = null;
+    private ?string $unitCode = UnitCode::UNIT;
+    private ?string $unitCodeListId = null;
+    private ?TaxTotal $taxTotal = null;
+    private ?InvoicePeriod $invoicePeriod = null;
+    private ?OrderLineReference $orderLineReference = null;
+    private ?string $note = null;
+    private ?Item $item = null;
+    private ?Price $price = null;
+    private ?string $accountingCostCode = null;
+    private ?string $accountingCost = null;
     /** @var AllowanceCharge[] $allowanceCharges */
-    private $allowanceCharges;
+    private ?array $allowanceCharges = null;
 
     private function isCreditNoteLine(): bool
     {
@@ -40,7 +40,7 @@ private function isDebitNoteLine(): bool
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getId(): ?string
     {
@@ -48,7 +48,7 @@ public function getId(): ?string
     }
 
     /**
-     * @param string $id
+     * @param string|null $id
      * @return static
      */
     public function setId(?string $id)
@@ -58,7 +58,7 @@ public function setId(?string $id)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getInvoicedQuantity(): ?float
     {
@@ -76,7 +76,7 @@ public function setInvoicedQuantity(?float $invoicedQuantity)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getLineExtensionAmount(): ?float
     {
@@ -84,7 +84,7 @@ public function getLineExtensionAmount(): ?float
     }
 
     /**
-     * @param float $lineExtensionAmount
+     * @param float|null $lineExtensionAmount
      * @return static
      */
     public function setLineExtensionAmount(?float $lineExtensionAmount)
@@ -94,7 +94,7 @@ public function setLineExtensionAmount(?float $lineExtensionAmount)
     }
 
     /**
-     * @return TaxTotal
+     * @return TaxTotal|null
      */
     public function getTaxTotal(): ?TaxTotal
     {
@@ -102,7 +102,7 @@ public function getTaxTotal(): ?TaxTotal
     }
 
     /**
-     * @param TaxTotal $taxTotal
+     * @param TaxTotal|null $taxTotal
      * @return static
      */
     public function setTaxTotal(?TaxTotal $taxTotal)
@@ -112,7 +112,7 @@ public function setTaxTotal(?TaxTotal $taxTotal)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getNote(): ?string
     {
@@ -120,7 +120,7 @@ public function getNote(): ?string
     }
 
     /**
-     * @param string $note
+     * @param string|null $note
      * @return static
      */
     public function setNote(?string $note)
@@ -130,7 +130,7 @@ public function setNote(?string $note)
     }
 
     /**
-     * @return InvoicePeriod
+     * @return InvoicePeriod|null
      */
     public function getInvoicePeriod(): ?InvoicePeriod
     {
@@ -138,7 +138,7 @@ public function getInvoicePeriod(): ?InvoicePeriod
     }
 
     /**
-     * @param InvoicePeriod $invoicePeriod
+     * @param InvoicePeriod|null $invoicePeriod
      * @return static
      */
     public function setInvoicePeriod(?InvoicePeriod $invoicePeriod)
@@ -148,7 +148,7 @@ public function setInvoicePeriod(?InvoicePeriod $invoicePeriod)
     }
 
     /**
-     * @return string
+     * @return OrderLineReference|null
      */
     public function getOrderLineReference(): ?OrderLineReference
     {
@@ -156,7 +156,7 @@ public function getOrderLineReference(): ?OrderLineReference
     }
 
     /**
-     * @param ?string $orderLineReference
+     * @param OrderLineReference|null $orderLineReference
      * @return static
      */
     public function setOrderLineReference(?OrderLineReference $orderLineReference)
@@ -166,7 +166,7 @@ public function setOrderLineReference(?OrderLineReference $orderLineReference)
     }
 
     /**
-     * @return Item
+     * @return Item|null
      */
     public function getItem(): ?Item
     {
@@ -174,7 +174,7 @@ public function getItem(): ?Item
     }
 
     /**
-     * @param Item $item
+     * @param Item|null $item
      * @return static
      */
     public function setItem(?Item $item)
@@ -184,7 +184,7 @@ public function setItem(?Item $item)
     }
 
     /**
-     * @return Price
+     * @return Price|null
      */
     public function getPrice(): ?Price
     {
@@ -192,7 +192,7 @@ public function getPrice(): ?Price
     }
 
     /**
-     * @param Price $price
+     * @param Price|null $price
      * @return static
      */
     public function setPrice(?Price $price)
@@ -202,7 +202,7 @@ public function setPrice(?Price $price)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getUnitCode(): ?string
     {
@@ -210,7 +210,7 @@ public function getUnitCode(): ?string
     }
 
     /**
-     * @param string $unitCode
+     * @param string|null $unitCode
      * @return static
      */
     public function setUnitCode(?string $unitCode)
@@ -220,7 +220,7 @@ public function setUnitCode(?string $unitCode)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getUnitCodeListId(): ?string
     {
@@ -228,7 +228,7 @@ public function getUnitCodeListId(): ?string
     }
 
     /**
-     * @param string $unitCodeListId
+     * @param string|null $unitCodeListId
      * @return static
      */
     public function setUnitCodeListId(?string $unitCodeListId)
@@ -238,7 +238,7 @@ public function setUnitCodeListId(?string $unitCodeListId)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getAccountingCostCode(): ?string
     {
@@ -246,7 +246,7 @@ public function getAccountingCostCode(): ?string
     }
 
     /**
-     * @param string $accountingCostCode
+     * @param string|null $accountingCostCode
      * @return static
      */
     public function setAccountingCostCode(?string $accountingCostCode)
@@ -256,7 +256,7 @@ public function setAccountingCostCode(?string $accountingCostCode)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getAccountingCost(): ?string
     {
@@ -264,7 +264,7 @@ public function getAccountingCost(): ?string
     }
 
     /**
-     * @param string $accountingCost
+     * @param string|null $accountingCost
      * @return static
      */
     public function setAccountingCost(?string $accountingCost)
@@ -274,7 +274,7 @@ public function setAccountingCost(?string $accountingCost)
     }
 
     /**
-     * @return AllowanceCharge[]
+     * @return AllowanceCharge[]|null
      */
     public function getAllowanceCharges(): ?array
     {
@@ -403,13 +403,21 @@ protected static function deserializedTag(array $mixedContent)
     {
         $collection = new ArrayCollection($mixedContent);
 
+        $invoicedQuantity = ReaderHelper::getTagValue(Schema::CBC . 'InvoicedQuantity', $collection) !== null
+            ? floatval(ReaderHelper::getTagValue(Schema::CBC . 'InvoicedQuantity', $collection))
+            : null;
+
+        $lineExtensionAmount = ReaderHelper::getTagValue(Schema::CBC . 'LineExtensionAmount', $collection) !== null
+            ? floatval(ReaderHelper::getTagValue(Schema::CBC . 'LineExtensionAmount', $collection))
+            : null;
+
         /** @var ?AllowanceCharge[] ReaderHelper::getArrayValue */
         $allowanceCharges = ReaderHelper::getArrayValue(Schema::CAC . 'AllowanceCharge', $collection);
 
         return (new static())
             ->setId(ReaderHelper::getTagValue(Schema::CBC . 'ID', $collection))
-            ->setInvoicedQuantity(ReaderHelper::getTagValue(Schema::CBC . 'InvoicedQuantity', $collection) !== null ? floatval(ReaderHelper::getTagValue(Schema::CBC . 'InvoicedQuantity', $collection)) : null)
-            ->setLineExtensionAmount(ReaderHelper::getTagValue(Schema::CBC . 'LineExtensionAmount', $collection) !== null ? floatval(ReaderHelper::getTagValue(Schema::CBC . 'LineExtensionAmount', $collection)) : null)
+            ->setInvoicedQuantity($invoicedQuantity)
+            ->setLineExtensionAmount($lineExtensionAmount)
             ->setTaxTotal(ReaderHelper::getTagValue(Schema::CAC . 'TaxTotal', $collection))
             ->setNote(ReaderHelper::getTagValue(Schema::CBC . 'Note', $collection))
             ->setInvoicePeriod(ReaderHelper::getTagValue(Schema::CAC . 'InvoicePeriod', $collection))
diff --git a/src/InvoicePeriod.php b/src/InvoicePeriod.php
index dbc28b6..bb6bfbb 100644
--- a/src/InvoicePeriod.php
+++ b/src/InvoicePeriod.php
@@ -15,12 +15,12 @@
 
 class InvoicePeriod implements XmlSerializable, XmlDeserializable
 {
-    private $startDate;
-    private $endDate;
-    private $descriptionCode;
+    private ?DateTime $startDate = null;
+    private ?DateTime $endDate = null;
+    private ?int $descriptionCode = null;
 
     /**
-     * @return DateTime
+     * @return DateTime|null
      */
     public function getStartDate(): ?DateTime
     {
@@ -28,7 +28,7 @@ public function getStartDate(): ?DateTime
     }
 
     /**
-     * @param DateTime $startDate
+     * @param DateTime|null $startDate
      * @return static
      */
     public function setStartDate(?DateTime $startDate)
@@ -38,7 +38,7 @@ public function setStartDate(?DateTime $startDate)
     }
 
     /**
-     * @return DateTime
+     * @return DateTime|null
      */
     public function getEndDate(): ?DateTime
     {
@@ -46,7 +46,7 @@ public function getEndDate(): ?DateTime
     }
 
     /**
-     * @param DateTime $endDate
+     * @param DateTime|null $endDate
      * @return static
      */
     public function setEndDate(?DateTime $endDate)
@@ -56,7 +56,7 @@ public function setEndDate(?DateTime $endDate)
     }
 
     /**
-     * @return int
+     * @return int|null
      */
     public function getDescriptionCode(): ?int
     {
@@ -64,7 +64,7 @@ public function getDescriptionCode(): ?int
     }
 
     /**
-     * @param Integer $descriptionCode
+     * @param int|null $descriptionCode
      * @return static
      */
     public function setDescriptionCode(?int $descriptionCode)
@@ -76,8 +76,8 @@ public function setDescriptionCode(?int $descriptionCode)
     /**
      * The validate function that is called during xml writing to valid the data of the object.
      *
-     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      * @return void
+     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      */
     public function validate()
     {
@@ -115,17 +115,28 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
     {
         $keyValues = keyValue($reader);
 
+        $startDate = isset($keyValues[Schema::CBC . 'StartDate'])
+            ? Carbon::parse($keyValues[Schema::CBC . 'StartDate'])->toDateTime()
+            : null;
+
+        $endDate = isset($keyValues[Schema::CBC . 'EndDate'])
+            ? Carbon::parse($keyValues[Schema::CBC . 'EndDate'])->toDateTime()
+            : null;
+
+        $descriptionCode = isset($keyValues[Schema::CBC . 'DescriptionCode'])
+            ? intval($keyValues[Schema::CBC . 'DescriptionCode'])
+            : null;
+
         return (new static())
-            ->setStartDate(isset($keyValues[Schema::CBC . 'StartDate']) ? Carbon::parse($keyValues[Schema::CBC . 'StartDate'])->toDateTime() : null)
-            ->setEndDate(isset($keyValues[Schema::CBC . 'EndDate']) ? Carbon::parse($keyValues[Schema::CBC . 'EndDate'])->toDateTime() : null)
-            ->setDescriptionCode(isset($keyValues[Schema::CBC . 'DescriptionCode']) ? intval($keyValues[Schema::CBC . 'DescriptionCode']) : null)
-        ;
+            ->setStartDate($startDate)
+            ->setEndDate($endDate)
+            ->setDescriptionCode($descriptionCode);
     }
 }
diff --git a/src/Item.php b/src/Item.php
index 957f01f..7519e9a 100644
--- a/src/Item.php
+++ b/src/Item.php
@@ -12,19 +12,19 @@
 
 class Item implements XmlSerializable, XmlDeserializable
 {
-    private $description;
-    private $name;
-    private $buyersItemIdentification;
-    private $sellersItemIdentification;
-    private $standardItemIdentification;
-    private $standardItemIdentificationAttributes = [];
-    private $commodityClassification;
-    private $classifiedTaxCategory;
-    private $originCountry;
-    private $additionalItemProperties;
+    private ?string $description = null;
+    private ?string $name = null;
+    private ?string $buyersItemIdentification = null;
+    private ?string $sellersItemIdentification = null;
+    private ?string $standardItemIdentification = null;
+    private array $standardItemIdentificationAttributes = [];
+    private ?CommodityClassification $commodityClassification = null;
+    private ?ClassifiedTaxCategory $classifiedTaxCategory = null;
+    private ?Country $originCountry = null;
+    private ?array $additionalItemProperties = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getDescription(): ?string
     {
@@ -32,7 +32,7 @@ public function getDescription(): ?string
     }
 
     /**
-     * @param string $description
+     * @param string|null $description
      * @return static
      */
     public function setDescription(?string $description)
@@ -42,7 +42,7 @@ public function setDescription(?string $description)
     }
 
     /**
-     * @return mixed
+     * @return string|null
      */
     public function getName(): ?string
     {
@@ -50,7 +50,7 @@ public function getName(): ?string
     }
 
     /**
-     * @param mixed $name
+     * @param string|null $name
      * @return static
      */
     public function setName(?string $name)
@@ -60,7 +60,7 @@ public function setName(?string $name)
     }
 
     /**
-     * @return mixed
+     * @return string|null
      */
     public function getSellersItemIdentification(): ?string
     {
@@ -68,7 +68,7 @@ public function getSellersItemIdentification(): ?string
     }
 
     /**
-     * @param mixed $sellersItemIdentification
+     * @param string|null $sellersItemIdentification
      * @return static
      */
     public function setSellersItemIdentification(?string $sellersItemIdentification)
@@ -78,7 +78,7 @@ public function setSellersItemIdentification(?string $sellersItemIdentification)
     }
 
     /**
-     * @return mixed
+     * @return string|null
      */
     public function getStandardItemIdentification(): ?string
     {
@@ -86,10 +86,11 @@ public function getStandardItemIdentification(): ?string
     }
 
     /**
-     * @param mixed $standardItemIdentification
+     * @param string|null $standardItemIdentification
+     * @param array|null $attributes
      * @return static
      */
-    public function setStandardItemIdentification(?string $standardItemIdentification, $attributes = null)
+    public function setStandardItemIdentification(?string $standardItemIdentification, array $attributes = null)
     {
         $this->standardItemIdentification = $standardItemIdentification;
         if (isset($attributes)) {
@@ -99,7 +100,7 @@ public function setStandardItemIdentification(?string $standardItemIdentificatio
     }
 
     /**
-     * @return CommodityClassification
+     * @return CommodityClassification|null
      */
     public function getCommodityClassification(): ?CommodityClassification
     {
@@ -117,7 +118,7 @@ public function setCommodityClassification(?CommodityClassification $commodityCl
     }
 
     /**
-     * @return mixed
+     * @return string|null
      */
     public function getBuyersItemIdentification(): ?string
     {
@@ -125,7 +126,7 @@ public function getBuyersItemIdentification(): ?string
     }
 
     /**
-     * @param mixed $buyersItemIdentification
+     * @param string|null $buyersItemIdentification
      * @return static
      */
     public function setBuyersItemIdentification(?string $buyersItemIdentification)
@@ -135,7 +136,7 @@ public function setBuyersItemIdentification(?string $buyersItemIdentification)
     }
 
     /**
-     * @return ClassifiedTaxCategory
+     * @return ClassifiedTaxCategory|null
      */
     public function getClassifiedTaxCategory(): ?ClassifiedTaxCategory
     {
@@ -143,7 +144,7 @@ public function getClassifiedTaxCategory(): ?ClassifiedTaxCategory
     }
 
     /**
-     * @param ClassifiedTaxCategory $classifiedTaxCategory
+     * @param ClassifiedTaxCategory|null $classifiedTaxCategory
      * @return static
      */
     public function setClassifiedTaxCategory(?ClassifiedTaxCategory $classifiedTaxCategory)
@@ -153,7 +154,7 @@ public function setClassifiedTaxCategory(?ClassifiedTaxCategory $classifiedTaxCa
     }
 
     /**
-     * @return Country
+     * @return Country|null
      */
     public function getOriginCountry(): ?Country
     {
@@ -161,7 +162,7 @@ public function getOriginCountry(): ?Country
     }
 
     /**
-     * @param Country $originCountry
+     * @param Country|null $originCountry
      * @return Item
      */
     public function setOriginCountry(?Country $originCountry): Item
@@ -171,7 +172,7 @@ public function setOriginCountry(?Country $originCountry): Item
     }
 
     /**
-     * @return AdditionalItemProperty[]
+     * @return AdditionalItemProperty[]|null
      */
     public function getAdditionalItemProperties(): ?array
     {
@@ -262,7 +263,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -275,7 +276,10 @@ public static function xmlDeserialize(Reader $reader)
         $classifiedTaxCategoryTag = ReaderHelper::getTag(Schema::CAC . 'ClassifiedTaxCategory', $collection);
         $commodityClassification = ReaderHelper::getTag(Schema::CAC . 'CommodityClassification', $collection);
         $originCountryTag = ReaderHelper::getTag(Schema::CAC . 'OriginCountry', $collection);
-        $additionalItemPropertiesTags = ReaderHelper::getArrayValue(Schema::CAC . 'AdditionalItemProperty', $collection);
+        $additionalItemPropertiesTags = ReaderHelper::getArrayValue(
+            Schema::CAC . 'AdditionalItemProperty',
+            $collection
+        );
 
         $buyersItemIdentificationTag = ReaderHelper::getTag(Schema::CAC . 'BuyersItemIdentification', $collection);
         $buyersItemIdentificationIdTag = ReaderHelper::getTag(
@@ -295,16 +299,18 @@ public static function xmlDeserialize(Reader $reader)
             new ArrayCollection($standardItemIdentificationTag['value'] ?? [])
         );
 
+        $standardItemIdentificationValue = $standardItemIdentificationIdTag['value'] ?? null;
+        $standardItemIdentificationAttributes = $standardItemIdentificationIdTag['attributes'] ?? null;
+
         return (new static())
             ->setDescription($descriptionTag['value'] ?? null)
             ->setName($nameTag['value'] ?? null)
             ->setBuyersItemIdentification($buyersItemIdentificationIdTag['value'] ?? null)
             ->setSellersItemIdentification($sellersItemIdentificationIdTag['value'] ?? null)
-            ->setStandardItemIdentification($standardItemIdentificationIdTag['value'] ?? null, $standardItemIdentificationIdTag['attributes'] ?? null)
+            ->setStandardItemIdentification($standardItemIdentificationValue, $standardItemIdentificationAttributes)
             ->setClassifiedTaxCategory($classifiedTaxCategoryTag['value'] ?? null)
             ->setCommodityClassification($commodityClassification['value'] ?? null)
             ->setOriginCountry($originCountryTag['value'] ?? null)
-            ->setAdditionalItemProperties($additionalItemPropertiesTags)
-        ;
+            ->setAdditionalItemProperties($additionalItemPropertiesTags);
     }
 }
diff --git a/src/LegalEntity.php b/src/LegalEntity.php
index 28bfe96..938a49a 100644
--- a/src/LegalEntity.php
+++ b/src/LegalEntity.php
@@ -12,14 +12,14 @@
 
 class LegalEntity implements XmlSerializable, XmlDeserializable
 {
-    private $registrationName;
-    private $companyId;
-    private $companyIdAttributes;
-    private $companyLegalForm;
-    private $companyLegalFormAttributes;
+    private ?string $registrationName = null;
+    private ?string $companyId = null;
+    private ?array $companyIdAttributes = null;
+    private ?string $companyLegalForm = null;
+    private ?array $companyLegalFormAttributes = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getRegistrationName(): ?string
     {
@@ -27,7 +27,7 @@ public function getRegistrationName(): ?string
     }
 
     /**
-     * @param string $registrationName
+     * @param string|null $registrationName
      * @return static
      */
     public function setRegistrationName(?string $registrationName)
@@ -37,7 +37,7 @@ public function setRegistrationName(?string $registrationName)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getCompanyId(): ?string
     {
@@ -45,10 +45,11 @@ public function getCompanyId(): ?string
     }
 
     /**
-     * @param string $companyId
+     * @param string|null $companyId
+     * @param array|null $attributes
      * @return static
      */
-    public function setCompanyId(?string $companyId, $attributes = null)
+    public function setCompanyId(?string $companyId, array $attributes = null)
     {
         $this->companyId = $companyId;
 
@@ -74,11 +75,11 @@ public function getCompanyIdSchemeId(): ?string
     }
 
     /**
-    *
-     * @param string $legalForm
+     * @param string|null $legalForm
+     * @param array|null $attributes
      * @return static
-    */
-    public function setCompanyLegalForm(?string $legalForm, $attributes = null)
+     */
+    public function setCompanyLegalForm(?string $legalForm, array $attributes = null)
     {
         $this->companyLegalForm = $legalForm;
 
@@ -123,7 +124,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -144,7 +145,6 @@ public static function xmlDeserialize(Reader $reader)
             ->setCompanyLegalForm(
                 $companyLegalForm['value'] ?? null,
                 $companyLegalForm['attributes'] ?? null
-            )
-        ;
+            );
     }
 }
diff --git a/src/LegalMonetaryTotal.php b/src/LegalMonetaryTotal.php
index 4abcd76..f8d27d0 100644
--- a/src/LegalMonetaryTotal.php
+++ b/src/LegalMonetaryTotal.php
@@ -11,17 +11,17 @@
 
 class LegalMonetaryTotal implements XmlSerializable, XmlDeserializable
 {
-    private $lineExtensionAmount = 0;
-    private $taxExclusiveAmount = 0;
-    private $taxInclusiveAmount = 0;
-    private $allowanceTotalAmount;
-    private $chargeTotalAmount;
-    private $prepaidAmount;
-    private $payableAmount = 0;
-    private $payableRoundingAmount;
+    private ?float $lineExtensionAmount = 0;
+    private ?float $taxExclusiveAmount = 0;
+    private ?float $taxInclusiveAmount = 0;
+    private ?float $allowanceTotalAmount = null;
+    private ?float $chargeTotalAmount = null;
+    private ?float $prepaidAmount = null;
+    private ?float $payableAmount = 0;
+    private ?float $payableRoundingAmount = null;
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getLineExtensionAmount(): ?float
     {
@@ -29,7 +29,7 @@ public function getLineExtensionAmount(): ?float
     }
 
     /**
-     * @param float $lineExtensionAmount
+     * @param float|null $lineExtensionAmount
      * @return static
      */
     public function setLineExtensionAmount(?float $lineExtensionAmount)
@@ -39,7 +39,7 @@ public function setLineExtensionAmount(?float $lineExtensionAmount)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getTaxExclusiveAmount(): ?float
     {
@@ -47,7 +47,7 @@ public function getTaxExclusiveAmount(): ?float
     }
 
     /**
-     * @param float $taxExclusiveAmount
+     * @param float|null $taxExclusiveAmount
      * @return static
      */
     public function setTaxExclusiveAmount(?float $taxExclusiveAmount)
@@ -57,7 +57,7 @@ public function setTaxExclusiveAmount(?float $taxExclusiveAmount)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getTaxInclusiveAmount(): ?float
     {
@@ -65,7 +65,7 @@ public function getTaxInclusiveAmount(): ?float
     }
 
     /**
-     * @param float $taxInclusiveAmount
+     * @param float|null $taxInclusiveAmount
      * @return static
      */
     public function setTaxInclusiveAmount(?float $taxInclusiveAmount)
@@ -75,7 +75,7 @@ public function setTaxInclusiveAmount(?float $taxInclusiveAmount)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getAllowanceTotalAmount(): ?float
     {
@@ -83,7 +83,7 @@ public function getAllowanceTotalAmount(): ?float
     }
 
     /**
-     * @param float $allowanceTotalAmount
+     * @param float|null $allowanceTotalAmount
      * @return static
      */
     public function setAllowanceTotalAmount(?float $allowanceTotalAmount)
@@ -93,7 +93,7 @@ public function setAllowanceTotalAmount(?float $allowanceTotalAmount)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getChargeTotalAmount(): ?float
     {
@@ -101,7 +101,7 @@ public function getChargeTotalAmount(): ?float
     }
 
     /**
-     * @param float $chargeTotalAmount
+     * @param float|null $chargeTotalAmount
      * @return static
      */
     public function setChargeTotalAmount(?float $chargeTotalAmount)
@@ -111,7 +111,7 @@ public function setChargeTotalAmount(?float $chargeTotalAmount)
     }
 
     /**
-     * @return ?float
+     * @return float|null
      */
     public function getPrepaidAmount(): ?float
     {
@@ -129,7 +129,7 @@ public function setPrepaidAmount(?float $prepaidAmount)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getPayableAmount(): ?float
     {
@@ -137,7 +137,7 @@ public function getPayableAmount(): ?float
     }
 
     /**
-     * @param float $payableAmount
+     * @param float|null $payableAmount
      * @return static
      */
     public function setPayableAmount(?float $payableAmount)
@@ -146,6 +146,9 @@ public function setPayableAmount(?float $payableAmount)
         return $this;
     }
 
+    /**
+     * @return float|null
+     */
     public function getPayableRoundingAmount(): ?float
     {
         return $this->payableRoundingAmount;
@@ -256,25 +259,51 @@ public function xmlSerialize(Writer $writer): void
     }
 
 
-
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
     {
         $keyValues = keyValue($reader);
 
+        $lineExtensionAmount = isset($keyValues[Schema::CBC . 'LineExtensionAmount'])
+            ? floatval($keyValues[Schema::CBC . 'LineExtensionAmount'])
+            : null;
+
+        $taxExclusiveAmount = isset($keyValues[Schema::CBC . 'TaxExclusiveAmount'])
+            ? floatval($keyValues[Schema::CBC . 'TaxExclusiveAmount'])
+            : null;
+
+        $taxInclusiveAmount = isset($keyValues[Schema::CBC . 'TaxInclusiveAmount'])
+            ? floatval($keyValues[Schema::CBC . 'TaxInclusiveAmount'])
+            : null;
+
+        $allowanceTotalAmount = isset($keyValues[Schema::CBC . 'AllowanceTotalAmount'])
+            ? floatval($keyValues[Schema::CBC . 'AllowanceTotalAmount'])
+            : null;
+
+        $chargeTotalAmount = isset($keyValues[Schema::CBC . 'ChargeTotalAmount'])
+            ? floatval($keyValues[Schema::CBC . 'ChargeTotalAmount'])
+            : null;
+
+        $prepaidAmount = isset($keyValues[Schema::CBC . 'PrepaidAmount'])
+            ? floatval($keyValues[Schema::CBC . 'PrepaidAmount'])
+            : null;
+
+        $payableAmount = isset($keyValues[Schema::CBC . 'PayableAmount'])
+            ? floatval($keyValues[Schema::CBC . 'PayableAmount'])
+            : null;
+
         return (new static())
-            ->setLineExtensionAmount(isset($keyValues[Schema::CBC . 'LineExtensionAmount']) ? floatval($keyValues[Schema::CBC . 'LineExtensionAmount']) : null)
-            ->setTaxExclusiveAmount(isset($keyValues[Schema::CBC . 'TaxExclusiveAmount']) ? floatval($keyValues[Schema::CBC . 'TaxExclusiveAmount']) : null)
-            ->setTaxInclusiveAmount(isset($keyValues[Schema::CBC . 'TaxInclusiveAmount']) ? floatval($keyValues[Schema::CBC . 'TaxInclusiveAmount']) : null)
-            ->setAllowanceTotalAmount(isset($keyValues[Schema::CBC . 'AllowanceTotalAmount']) ? floatval($keyValues[Schema::CBC . 'AllowanceTotalAmount']) : null)
-            ->setChargeTotalAmount(isset($keyValues[Schema::CBC . 'ChargeTotalAmount']) ? floatval($keyValues[Schema::CBC . 'ChargeTotalAmount']) : null)
-            ->setPrepaidAmount(isset($keyValues[Schema::CBC . 'PrepaidAmount']) ? floatval($keyValues[Schema::CBC . 'PrepaidAmount']) : null)
-            ->setPayableRoundingAmount(isset($keyValues[Schema::CBC . 'PayableAmount']) ? floatval($keyValues[Schema::CBC . 'PayableAmount']) : null)
-            ->setPayableAmount(isset($keyValues[Schema::CBC . 'PayableAmount']) ? floatval($keyValues[Schema::CBC . 'PayableAmount']) : null)
-        ;
+            ->setLineExtensionAmount($lineExtensionAmount)
+            ->setTaxExclusiveAmount($taxExclusiveAmount)
+            ->setTaxInclusiveAmount($taxInclusiveAmount)
+            ->setAllowanceTotalAmount($allowanceTotalAmount)
+            ->setChargeTotalAmount($chargeTotalAmount)
+            ->setPrepaidAmount($prepaidAmount)
+            ->setPayableRoundingAmount($payableAmount)
+            ->setPayableAmount($payableAmount);
     }
 }
diff --git a/src/NumberFormatter.php b/src/NumberFormatter.php
index 3fe3e6f..9e553c4 100644
--- a/src/NumberFormatter.php
+++ b/src/NumberFormatter.php
@@ -11,7 +11,7 @@ class NumberFormatter
      * @param int|null $decimals
      * @param string $decimalSeparator
      * @param string $thousandsSeparator
-     * @return void
+     * @return string
      */
     public static function format(
         $number,
@@ -32,13 +32,11 @@ public static function format(
             $decimals = isset($parts[1]) ? strlen(rtrim($parts[1], "0")) : 0;
         }
 
-        $value = number_format(
+        return number_format(
             $number,
             $decimals,
             $decimalSeparator,
             $thousandsSeparator
         );
-
-        return $value;
     }
 }
diff --git a/src/OrderLineReference.php b/src/OrderLineReference.php
index d5481bd..8b2e8a9 100644
--- a/src/OrderLineReference.php
+++ b/src/OrderLineReference.php
@@ -16,10 +16,10 @@
  */
 class OrderLineReference implements XmlSerializable, XmlDeserializable
 {
-    private $lineId;
+    private ?string $lineId = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getLineId(): ?string
     {
@@ -27,7 +27,7 @@ public function getLineId(): ?string
     }
 
     /**
-     * @param string $lineId
+     * @param string|null $lineId
      * @return static
      */
     public function setLineId(?string $lineId)
@@ -60,7 +60,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -68,7 +68,6 @@ public static function xmlDeserialize(Reader $reader)
         $keyValues = keyValue($reader);
 
         return (new static())
-            ->setLineId($keyValues[Schema::CBC . 'LineID'] ?? null)
-        ;
+            ->setLineId($keyValues[Schema::CBC . 'LineID'] ?? null);
     }
 }
diff --git a/src/OrderReference.php b/src/OrderReference.php
index 099c25a..fa7e417 100644
--- a/src/OrderReference.php
+++ b/src/OrderReference.php
@@ -14,9 +14,9 @@
 
 class OrderReference implements XmlSerializable, XmlDeserializable
 {
-    private $id;
-    private $salesOrderId;
-    private $issueDate;
+    private ?string $id = null;
+    private string $salesOrderId;
+    private ?DateTime $issueDate = null;
 
     /**
      * @return string|null
@@ -45,7 +45,7 @@ public function getSalesOrderId(): string
     }
 
     /**
-     * @return DateTime
+     * @return DateTime|null
      */
     public function getIssueDate(): ?DateTime
     {
@@ -53,7 +53,7 @@ public function getIssueDate(): ?DateTime
     }
 
     /**
-     * @param DateTime $issueDate
+     * @param DateTime|null $issueDate
      * @return static
      */
     public function setIssueDate(?DateTime $issueDate)
@@ -63,7 +63,7 @@ public function setIssueDate(?DateTime $issueDate)
     }
 
     /**
-     * @param string $salesOrderId
+     * @param string|null $salesOrderId
      * @return static
      */
     public function setSalesOrderId(?string $salesOrderId)
@@ -95,17 +95,20 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
     {
         $keyValues = keyValue($reader);
 
+        $issueDate = isset($keyValues[Schema::CBC . 'IssueDate'])
+            ? Carbon::parse($keyValues[Schema::CBC . 'IssueDate'])->toDateTime()
+            : null;
+
         return (new static())
             ->setId($keyValues[Schema::CBC . 'ID'] ?? null)
-            ->setIssueDate(isset($keyValues[Schema::CBC . 'IssueDate']) ? Carbon::parse($keyValues[Schema::CBC . 'IssueDate'])->toDateTime() : null)
-            ->setSalesOrderId($keyValues[Schema::CBC . 'SalesOrderID'] ?? null)
-        ;
+            ->setIssueDate($issueDate)
+            ->setSalesOrderId($keyValues[Schema::CBC . 'SalesOrderID'] ?? null);
     }
 }
diff --git a/src/OriginatorDocumentReference.php b/src/OriginatorDocumentReference.php
index ef51444..4738dba 100644
--- a/src/OriginatorDocumentReference.php
+++ b/src/OriginatorDocumentReference.php
@@ -17,10 +17,10 @@
  */
 class OriginatorDocumentReference implements XmlSerializable, XmlDeserializable
 {
-    private $id;
+    private ?string $id = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getId(): ?string
     {
@@ -28,7 +28,7 @@ public function getId(): ?string
     }
 
     /**
-     * @param string $id
+     * @param string|null $id
      * @return static
      */
     public function setId(?string $id)
diff --git a/src/Party.php b/src/Party.php
index 261b13c..779fce7 100644
--- a/src/Party.php
+++ b/src/Party.php
@@ -13,20 +13,20 @@
 
 class Party implements XmlSerializable, XmlDeserializable
 {
-    private $name;
-    private $partyIdentificationId;
-    private $partyIdentificationSchemeId;
-    private $partyIdentificationSchemeName;
-    private $postalAddress;
-    private $physicalLocation;
-    private $contact;
-    private $partyTaxScheme;
-    private $legalEntity;
-    private $endpointID;
-    private $endpointID_schemeID;
+    private ?string $name = null;
+    private ?string $partyIdentificationId = null;
+    private ?string $partyIdentificationSchemeId = null;
+    private ?string $partyIdentificationSchemeName = null;
+    private ?Address $postalAddress = null;
+    private ?Address $physicalLocation = null;
+    private ?Contact $contact = null;
+    private ?PartyTaxScheme $partyTaxScheme = null;
+    private ?LegalEntity $legalEntity = null;
+    private ?string $endpointID = null;
+    private ?string $endpointID_schemeID = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getName(): ?string
     {
@@ -34,7 +34,7 @@ public function getName(): ?string
     }
 
     /**
-     * @param string $name
+     * @param string|null $name
      * @return static
      */
     public function setName(?string $name)
@@ -44,7 +44,7 @@ public function setName(?string $name)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getPartyIdentificationId(): ?string
     {
@@ -52,7 +52,7 @@ public function getPartyIdentificationId(): ?string
     }
 
     /**
-     * @param string $partyIdentificationId
+     * @param string|null $partyIdentificationId
      * @return static
      */
     public function setPartyIdentificationId(?string $partyIdentificationId)
@@ -62,7 +62,7 @@ public function setPartyIdentificationId(?string $partyIdentificationId)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getPartyIdentificationSchemeId(): ?string
     {
@@ -70,7 +70,7 @@ public function getPartyIdentificationSchemeId(): ?string
     }
 
     /**
-     * @param string $partyIdentificationSchemeId
+     * @param string|null $partyIdentificationSchemeId
      * @return static
      */
     public function setPartyIdentificationSchemeId(?string $partyIdentificationSchemeId)
@@ -80,7 +80,7 @@ public function setPartyIdentificationSchemeId(?string $partyIdentificationSchem
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getPartyIdentificationSchemeName(): ?string
     {
@@ -88,7 +88,7 @@ public function getPartyIdentificationSchemeName(): ?string
     }
 
     /**
-     * @param string $partyIdentificationSchemeName
+     * @param string|null $partyIdentificationSchemeName
      * @return static
      */
     public function setPartyIdentificationSchemeName(?string $partyIdentificationSchemeName)
@@ -98,7 +98,7 @@ public function setPartyIdentificationSchemeName(?string $partyIdentificationSch
     }
 
     /**
-     * @return Address
+     * @return Address|null
      */
     public function getPostalAddress(): ?Address
     {
@@ -106,7 +106,7 @@ public function getPostalAddress(): ?Address
     }
 
     /**
-     * @param Address $postalAddress
+     * @param Address|null $postalAddress
      * @return static
      */
     public function setPostalAddress(?Address $postalAddress)
@@ -116,7 +116,7 @@ public function setPostalAddress(?Address $postalAddress)
     }
 
     /**
-     * @return LegalEntity
+     * @return LegalEntity|null
      */
     public function getLegalEntity(): ?LegalEntity
     {
@@ -124,7 +124,7 @@ public function getLegalEntity(): ?LegalEntity
     }
 
     /**
-     * @param LegalEntity $legalEntity
+     * @param LegalEntity|null $legalEntity
      * @return static
      */
     public function setLegalEntity(?LegalEntity $legalEntity)
@@ -134,7 +134,7 @@ public function setLegalEntity(?LegalEntity $legalEntity)
     }
 
     /**
-     * @return Address
+     * @return Address|null
      */
     public function getPhysicalLocation(): ?Address
     {
@@ -142,7 +142,7 @@ public function getPhysicalLocation(): ?Address
     }
 
     /**
-     * @param Address $physicalLocation
+     * @param Address|null $physicalLocation
      * @return static
      */
     public function setPhysicalLocation(?Address $physicalLocation)
@@ -152,7 +152,7 @@ public function setPhysicalLocation(?Address $physicalLocation)
     }
 
     /**
-     * @return staticTaxScheme
+     * @return PartyTaxScheme|null
      */
     public function getPartyTaxScheme(): ?PartyTaxScheme
     {
@@ -160,7 +160,7 @@ public function getPartyTaxScheme(): ?PartyTaxScheme
     }
 
     /**
-     * @param PartyTaxScheme $partyTaxScheme
+     * @param PartyTaxScheme|null $partyTaxScheme
      * @return static
      */
     public function setPartyTaxScheme(?PartyTaxScheme $partyTaxScheme)
@@ -170,7 +170,7 @@ public function setPartyTaxScheme(?PartyTaxScheme $partyTaxScheme)
     }
 
     /**
-     * @return Contact
+     * @return Contact|null
      */
     public function getContact(): ?Contact
     {
@@ -178,7 +178,7 @@ public function getContact(): ?Contact
     }
 
     /**
-     * @param Contact $contact
+     * @param Contact|null $contact
      * @return static
      */
     public function setContact(?Contact $contact)
@@ -199,11 +199,17 @@ public function setEndpointId($endpointID, $schemeID)
         return $this;
     }
 
+    /**
+     * @return string|null
+     */
     public function getEndpointId(): ?string
     {
         return $this->endpointID;
     }
 
+    /**
+     * @return string|null
+     */
     public function getEndpointIDSchemeId(): ?string
     {
         return $this->endpointID_schemeID;
@@ -287,7 +293,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -301,14 +307,20 @@ public static function xmlDeserialize(Reader $reader)
         $endpointId = ReaderHelper::getTag(Schema::CBC . 'EndpointID', $collection);
         $postalAddress = ReaderHelper::getTag(Schema::CAC . 'PostalAddress', $collection);
         $physicalLocation = ReaderHelper::getTag(Schema::CAC . 'PhysicalLocation', $collection);
-        $physicalLocationAddress = ReaderHelper::getTag(Schema::CAC . 'Address', new ArrayCollection($physicalLocation['value'] ?? []));
+        $physicalLocationAddress = ReaderHelper::getTag(
+            Schema::CAC . 'Address',
+            new ArrayCollection($physicalLocation['value'] ?? [])
+        );
 
         $partyTaxScheme = ReaderHelper::getTag(Schema::CAC . 'PartyTaxScheme', $collection);
         $partyLegalEntity = ReaderHelper::getTag(Schema::CAC . 'PartyLegalEntity', $collection);
         $partyContact = ReaderHelper::getTag(Schema::CAC . 'Contact', $collection);
 
         $partyIdentification = ReaderHelper::getTag(Schema::CAC . 'PartyIdentification', $collection);
-        $partyIdentificationId = ReaderHelper::getTag(Schema::CBC . 'ID', new ArrayCollection($partyIdentification['value'] ?? []));
+        $partyIdentificationId = ReaderHelper::getTag(
+            Schema::CBC . 'ID',
+            new ArrayCollection($partyIdentification['value'] ?? [])
+        );
 
         return (new static())
             ->setName($partyNameName['value'] ?? null)
@@ -320,7 +332,6 @@ public static function xmlDeserialize(Reader $reader)
             ->setEndpointId($endpointId['value'] ?? null, $endpointId['attributes']['schemeID'] ?? null)
             ->setPartyIdentificationId($partyIdentificationId['value'] ?? null)
             ->setPartyIdentificationSchemeId($partyIdentificationId['attributes']['schemeID'] ?? null)
-            ->setPartyIdentificationSchemeName($partyIdentificationId['attributes']['schemeName'] ?? null)
-        ;
+            ->setPartyIdentificationSchemeName($partyIdentificationId['attributes']['schemeName'] ?? null);
     }
 }
diff --git a/src/PartyTaxScheme.php b/src/PartyTaxScheme.php
index 6c5338f..b6e4623 100644
--- a/src/PartyTaxScheme.php
+++ b/src/PartyTaxScheme.php
@@ -13,12 +13,12 @@
 
 class PartyTaxScheme implements XmlSerializable, XmlDeserializable
 {
-    private $registrationName;
-    private $companyId;
-    private $taxScheme;
+    private ?string $registrationName = null;
+    private ?string $companyId = null;
+    private ?TaxScheme $taxScheme = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getRegistrationName(): ?string
     {
@@ -29,14 +29,14 @@ public function getRegistrationName(): ?string
      * @param string $registrationName
      * @return static
      */
-    public function setRegistrationName($registrationName)
+    public function setRegistrationName(string $registrationName)
     {
         $this->registrationName = $registrationName;
         return $this;
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getCompanyId(): ?string
     {
@@ -47,14 +47,14 @@ public function getCompanyId(): ?string
      * @param string $companyId
      * @return static
      */
-    public function setCompanyId($companyId)
+    public function setCompanyId(string $companyId)
     {
         $this->companyId = $companyId;
         return $this;
     }
 
     /**
-     * @return ?TaxScheme
+     * @return TaxScheme|null
      */
     public function getTaxScheme(): ?TaxScheme
     {
@@ -62,7 +62,7 @@ public function getTaxScheme(): ?TaxScheme
     }
 
     /**
-     * @param TaxScheme $taxScheme
+     * @param TaxScheme|null $taxScheme
      * @return static
      */
     public function setTaxScheme(?TaxScheme $taxScheme)
@@ -111,7 +111,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -121,7 +121,6 @@ public static function xmlDeserialize(Reader $reader)
         return (new static())
             ->setRegistrationName($keyValues[Schema::CBC . 'RegistrationName'] ?? null)
             ->setCompanyId($keyValues[Schema::CBC . 'CompanyID'] ?? null)
-            ->setTaxScheme($keyValues[Schema::CAC . 'TaxScheme'] ?? null)
-        ;
+            ->setTaxScheme($keyValues[Schema::CAC . 'TaxScheme'] ?? null);
     }
 }
diff --git a/src/PayeeFinancialAccount.php b/src/PayeeFinancialAccount.php
index 3e74c99..27b9e88 100644
--- a/src/PayeeFinancialAccount.php
+++ b/src/PayeeFinancialAccount.php
@@ -11,12 +11,12 @@
 
 class PayeeFinancialAccount implements XmlSerializable, XmlDeserializable
 {
-    private $id;
-    private $name;
-    private $financialInstitutionBranch;
+    private ?string $id = null;
+    private ?string $name = null;
+    private ?FinancialInstitutionBranch $financialInstitutionBranch = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getId(): ?string
     {
@@ -24,7 +24,7 @@ public function getId(): ?string
     }
 
     /**
-     * @param string $id
+     * @param string|null $id
      * @return static
      */
     public function setId(?string $id)
@@ -34,7 +34,7 @@ public function setId(?string $id)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getName(): ?string
     {
@@ -42,7 +42,7 @@ public function getName(): ?string
     }
 
     /**
-     * @param string $name
+     * @param string|null $name
      * @return static
      */
     public function setName(?string $name)
@@ -52,7 +52,7 @@ public function setName(?string $name)
     }
 
     /**
-     * @return FinancialInstitutionBranch
+     * @return FinancialInstitutionBranch|null
      */
     public function getFinancialInstitutionBranch(): ?FinancialInstitutionBranch
     {
@@ -60,7 +60,7 @@ public function getFinancialInstitutionBranch(): ?FinancialInstitutionBranch
     }
 
     /**
-     * @param FinancialInstitutionBranch $financialInstitutionBranch
+     * @param FinancialInstitutionBranch|null $financialInstitutionBranch
      * @return static
      */
     public function setFinancialInstitutionBranch(?FinancialInstitutionBranch $financialInstitutionBranch)
@@ -94,7 +94,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
diff --git a/src/PayeeParty.php b/src/PayeeParty.php
index ae3bfd0..bc6da10 100644
--- a/src/PayeeParty.php
+++ b/src/PayeeParty.php
@@ -12,14 +12,14 @@
 
 class PayeeParty implements XmlSerializable, XmlDeserializable
 {
-    private $partyIdentificationId;
-    private $partyIdentificationSchemeId;
-    private $partyName;
-    private $partyLegalEntityCompanyId;
-    private $partyLegalEntityCompanySchemeId;
+    private ?string $partyIdentificationId = null;
+    private ?string $partyIdentificationSchemeId = null;
+    private ?string $partyName = null;
+    private ?string $partyLegalEntityCompanyId = null;
+    private ?string $partyLegalEntityCompanySchemeId = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getPartyIdentificationId(): ?string
     {
@@ -37,7 +37,7 @@ public function setPartyIdentificationId(?string $partyIdentificationId)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getPartyIdentificationSchemeId(): ?string
     {
@@ -55,7 +55,7 @@ public function setPartyIdentificationSchemeId(?string $partyIdentificationSchem
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getPartyName(): ?string
     {
@@ -74,7 +74,7 @@ public function setPartyName(?string $partyName)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getPartyLegalEntityCompanyId(): ?string
     {
@@ -92,7 +92,7 @@ public function setPartyLegalEntityCompanyId(?string $partyLegalEntityCompanyId)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getPartyLegalEntityCompanySchemeId(): ?string
     {
@@ -161,7 +161,8 @@ public static function xmlDeserialize(Reader $reader)
         $collection = new ArrayCollection($mixedContent);
 
         $partyIdentification = ReaderHelper::getTag(Schema::CAC . 'PartyIdentification', $collection);
-        $partyIdentificationId = ReaderHelper::getTag(Schema::CBC . 'ID', new ArrayCollection($partyIdentification['value'] ?? []));
+        $partyIdentificationCollection = new ArrayCollection($partyIdentification['value'] ?? []);
+        $partyIdentificationId = ReaderHelper::getTag(Schema::CBC . 'ID', $partyIdentificationCollection);
 
         $partyName = ReaderHelper::getTag(Schema::CAC . 'PartyName', $collection);
         $partyNameName = ReaderHelper::getTag(Schema::CBC . 'Name', new ArrayCollection($partyName['value'] ?? []));
diff --git a/src/PaymentMandate.php b/src/PaymentMandate.php
index 8c1fd7d..03b5e27 100644
--- a/src/PaymentMandate.php
+++ b/src/PaymentMandate.php
@@ -11,13 +11,12 @@
 
 class PaymentMandate implements XmlSerializable, XmlDeserializable
 {
-    public $xmlTagName = 'PaymentMandate';
 
-    private $id;
-    private $payeeFinancialAccount;
+    private ?string $id = null;
+    private ?PayeeFinancialAccount $payeeFinancialAccount = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getId(): ?string
     {
@@ -25,7 +24,7 @@ public function getId(): ?string
     }
 
     /**
-     * @param string $id
+     * @param string|null $id
      * @return static
      */
     public function setId(?string $id)
@@ -35,7 +34,7 @@ public function setId(?string $id)
     }
 
     /**
-     * @return PayeeFinancialAccount
+     * @return PayeeFinancialAccount|null
      */
     public function getPayeeFinancialAccount(): ?PayeeFinancialAccount
     {
@@ -43,7 +42,7 @@ public function getPayeeFinancialAccount(): ?PayeeFinancialAccount
     }
 
     /**
-     * @param PayeeFinancialAccount $payeeFinancialAccount
+     * @param PayeeFinancialAccount|null $payeeFinancialAccount
      * @return static
      */
     public function setPayeeFinancialAccount(?PayeeFinancialAccount $payeeFinancialAccount)
diff --git a/src/PaymentMeans.php b/src/PaymentMeans.php
index 6e497d4..8bd5df8 100644
--- a/src/PaymentMeans.php
+++ b/src/PaymentMeans.php
@@ -14,21 +14,21 @@
 
 class PaymentMeans implements XmlSerializable, XmlDeserializable
 {
-    public $xmlTagName = 'PaymentMeans';
-    private $paymentMeansCode = UNCL4461::INSTRUMENT_NOT_DEFINED;
-    private $paymentMeansCodeAttributes = [
+    public string $xmlTagName = 'PaymentMeans';
+    private string $paymentMeansCode = UNCL4461::INSTRUMENT_NOT_DEFINED;
+    private array $paymentMeansCodeAttributes = [
         'listID'   => 'UN/ECE 4461',
         'listName' => 'Payment Means',
         'listURI'  => 'http://docs.oasis-open.org/ubl/os-UBL-2.0-update/cl/gc/default/PaymentMeansCode-2.0.gc'];
-    private $paymentDueDate;
-    private $instructionId;
-    private $instructionNote;
-    private $paymentId;
-    private $payeeFinancialAccount;
-    private $paymentMandate;
+    private ?DateTime $paymentDueDate = null;
+    private ?string $instructionId = null;
+    private ?string $instructionNote = null;
+    private ?string $paymentId = null;
+    private ?PayeeFinancialAccount $payeeFinancialAccount = null;
+    private ?PaymentMandate $paymentMandate = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getPaymentMeansCode(): ?string
     {
@@ -36,10 +36,11 @@ public function getPaymentMeansCode(): ?string
     }
 
     /**
-     * @param string $paymentMeansCode
+     * @param string|null $paymentMeansCode
+     * @param array|null $attributes
      * @return static
      */
-    public function setPaymentMeansCode(?string $paymentMeansCode, $attributes = null)
+    public function setPaymentMeansCode(?string $paymentMeansCode, array $attributes = null)
     {
         $this->paymentMeansCode = $paymentMeansCode;
         if (isset($attributes)) {
@@ -49,7 +50,7 @@ public function setPaymentMeansCode(?string $paymentMeansCode, $attributes = nul
     }
 
     /**
-     * @return DateTime
+     * @return DateTime|null
      */
     public function getPaymentDueDate(): ?DateTime
     {
@@ -57,7 +58,7 @@ public function getPaymentDueDate(): ?DateTime
     }
 
     /**
-     * @param DateTime $paymentDueDate
+     * @param DateTime|null $paymentDueDate
      * @return static
      */
     public function setPaymentDueDate(?DateTime $paymentDueDate)
@@ -67,7 +68,7 @@ public function setPaymentDueDate(?DateTime $paymentDueDate)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getInstructionId(): ?string
     {
@@ -75,7 +76,7 @@ public function getInstructionId(): ?string
     }
 
     /**
-     * @param string $instructionId
+     * @param string|null $instructionId
      * @return static
      */
     public function setInstructionId(?string $instructionId)
@@ -85,7 +86,7 @@ public function setInstructionId(?string $instructionId)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getInstructionNote(): ?string
     {
@@ -93,7 +94,7 @@ public function getInstructionNote(): ?string
     }
 
     /**
-     * @param string $instructionNote
+     * @param string|null $instructionNote
      * @return static
      */
     public function setInstructionNote(?string $instructionNote)
@@ -103,7 +104,7 @@ public function setInstructionNote(?string $instructionNote)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getPaymentId(): ?string
     {
@@ -111,7 +112,7 @@ public function getPaymentId(): ?string
     }
 
     /**
-     * @param string $paymentId
+     * @param string|null $paymentId
      * @return static
      */
     public function setPaymentId(?string $paymentId)
@@ -121,7 +122,7 @@ public function setPaymentId(?string $paymentId)
     }
 
     /**
-     * @return mixed
+     * @return PayeeFinancialAccount|null
      */
     public function getPayeeFinancialAccount(): ?PayeeFinancialAccount
     {
@@ -129,7 +130,7 @@ public function getPayeeFinancialAccount(): ?PayeeFinancialAccount
     }
 
     /**
-     * @param mixed $payeeFinancialAccount
+     * @param PayeeFinancialAccount|null $payeeFinancialAccount
      * @return static
      */
     public function setPayeeFinancialAccount(?PayeeFinancialAccount $payeeFinancialAccount)
@@ -139,7 +140,7 @@ public function setPayeeFinancialAccount(?PayeeFinancialAccount $payeeFinancialA
     }
 
     /**
-     * @return PaymentMandate
+     * @return PaymentMandate|null
      */
     public function getPaymentMandate(): ?PaymentMandate
     {
@@ -147,7 +148,7 @@ public function getPaymentMandate(): ?PaymentMandate
     }
 
     /**
-     * @param PaymentMandate $paymentMandate
+     * @param PaymentMandate|null $paymentMandate
      * @return static
      */
     public function setPaymentMandate(?PaymentMandate $paymentMandate)
@@ -203,16 +204,20 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
     {
         $keyValues = keyValue($reader);
 
+        $paymentDueDate = isset($keyValues[Schema::CBC . 'PaymentDueDate'])
+            ? Carbon::parse($keyValues[Schema::CBC . 'PaymentDueDate'])->toDateTime()
+            : null;
+
         return (new static())
             ->setPaymentMeansCode($keyValues[Schema::CBC . 'PaymentMeansCode'] ?? null)
-            ->setPaymentDueDate(isset($keyValues[Schema::CBC . 'PaymentDueDate']) ? Carbon::parse($keyValues[Schema::CBC . 'PaymentDueDate'])->toDateTime() : null)
+            ->setPaymentDueDate($paymentDueDate)
             ->setInstructionId($keyValues[Schema::CBC . 'InstructionID'] ?? null)
             ->setInstructionNote($keyValues[Schema::CBC . 'InstructionNote'] ?? null)
             ->setPaymentId($keyValues[Schema::CBC . 'PaymentID'] ?? null)
diff --git a/src/PaymentTerms.php b/src/PaymentTerms.php
index d6ae258..015e914 100644
--- a/src/PaymentTerms.php
+++ b/src/PaymentTerms.php
@@ -11,13 +11,13 @@
 
 class PaymentTerms implements XmlSerializable, XmlDeserializable
 {
-    private $note;
-    private $settlementDiscountPercent;
-    private $amount;
-    private $settlementPeriod;
+    private ?string $note = null;
+    private ?float $settlementDiscountPercent = null;
+    private ?float $amount = null;
+    private ?SettlementPeriod $settlementPeriod = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getNote(): ?string
     {
@@ -25,7 +25,7 @@ public function getNote(): ?string
     }
 
     /**
-     * @param string $note
+     * @param string|null $note
      * @return static
      */
     public function setNote(?string $note)
@@ -35,7 +35,7 @@ public function setNote(?string $note)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getSettlementDiscountPercent(): ?float
     {
@@ -43,7 +43,7 @@ public function getSettlementDiscountPercent(): ?float
     }
 
     /**
-     * @param float $settlementDiscountPercent
+     * @param float|null $settlementDiscountPercent
      * @return static
      */
     public function setSettlementDiscountPercent(?float $settlementDiscountPercent)
@@ -53,7 +53,7 @@ public function setSettlementDiscountPercent(?float $settlementDiscountPercent)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getAmount(): ?float
     {
@@ -61,7 +61,7 @@ public function getAmount(): ?float
     }
 
     /**
-     * @param float $amount
+     * @param float|null $amount
      * @return static
      */
     public function setAmount(?float $amount)
@@ -71,7 +71,7 @@ public function setAmount(?float $amount)
     }
 
     /**
-     * @return SettlementPeriod
+     * @return SettlementPeriod|null
      */
     public function getSettlementPeriod(): ?SettlementPeriod
     {
@@ -79,7 +79,7 @@ public function getSettlementPeriod(): ?SettlementPeriod
     }
 
     /**
-     * @param SettlementPeriod $settlementPeriod
+     * @param SettlementPeriod|null $settlementPeriod
      * @return static
      */
     public function setSettlementPeriod(?SettlementPeriod $settlementPeriod)
@@ -117,7 +117,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -128,7 +128,6 @@ public static function xmlDeserialize(Reader $reader)
             ->setNote($keyValues[Schema::CBC . 'Note'] ?? null)
             ->setSettlementDiscountPercent($keyValues[Schema::CBC . 'SettlementDiscountPercent'] ?? null)
             ->setAmount($keyValues[Schema::CBC . 'Amount'] ?? null)
-            ->setSettlementPeriod($keyValues[Schema::CAC . 'SettlementPeriod'] ?? null)
-        ;
+            ->setSettlementPeriod($keyValues[Schema::CAC . 'SettlementPeriod'] ?? null);
     }
 }
diff --git a/src/Price.php b/src/Price.php
index 77c5d67..b0f72c3 100644
--- a/src/Price.php
+++ b/src/Price.php
@@ -12,14 +12,14 @@
 
 class Price implements XmlSerializable, XmlDeserializable
 {
-    private $priceAmount;
-    private $baseQuantity;
-    private $unitCode = UnitCode::UNIT;
-    private $unitCodeListId;
-    private $allowanceCharge;
+    private ?float $priceAmount = null;
+    private ?float $baseQuantity = null;
+    private ?string $unitCode = UnitCode::UNIT;
+    private ?string $unitCodeListId = null;
+    private ?AllowanceCharge $allowanceCharge = null;
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getPriceAmount(): ?float
     {
@@ -27,7 +27,7 @@ public function getPriceAmount(): ?float
     }
 
     /**
-     * @param float $priceAmount
+     * @param float|null $priceAmount
      * @return static
      */
     public function setPriceAmount(?float $priceAmount)
@@ -37,7 +37,7 @@ public function setPriceAmount(?float $priceAmount)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getBaseQuantity(): ?float
     {
@@ -45,7 +45,7 @@ public function getBaseQuantity(): ?float
     }
 
     /**
-     * @param float $baseQuantity
+     * @param float|null $baseQuantity
      * @return static
      */
     public function setBaseQuantity(?float $baseQuantity)
@@ -55,7 +55,7 @@ public function setBaseQuantity(?float $baseQuantity)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getUnitCode(): ?string
     {
@@ -63,7 +63,7 @@ public function getUnitCode(): ?string
     }
 
     /**
-     * @param string $unitCode
+     * @param string|null $unitCode
      *                         See also: src/UnitCode.php
      * @return static
      */
@@ -75,7 +75,7 @@ public function setUnitCode(?string $unitCode)
 
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getUnitCodeListId(): ?string
     {
@@ -83,7 +83,7 @@ public function getUnitCodeListId(): ?string
     }
 
     /**
-     * @param string $unitCodeListId
+     * @param string|null $unitCodeListId
      * @return static
      */
     public function setUnitCodeListId(?string $unitCodeListId)
@@ -93,7 +93,7 @@ public function setUnitCodeListId(?string $unitCodeListId)
     }
 
     /**
-     * @return AllowanceCharge
+     * @return AllowanceCharge|null
      */
     public function getAllowanceCharge(): ?AllowanceCharge
     {
@@ -101,7 +101,7 @@ public function getAllowanceCharge(): ?AllowanceCharge
     }
 
     /**
-     * @param AllowanceCharge $allowanceCharge
+     * @param AllowanceCharge|null $allowanceCharge
      * @return static
      */
     public function setAllowanceCharge(?AllowanceCharge $allowanceCharge)
@@ -155,7 +155,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
diff --git a/src/ProjectReference.php b/src/ProjectReference.php
index 51beb17..b66547b 100644
--- a/src/ProjectReference.php
+++ b/src/ProjectReference.php
@@ -11,7 +11,7 @@
 
 class ProjectReference implements XmlSerializable, XmlDeserializable
 {
-    private $id;
+    private ?string $id = null;
 
     /**
      * @return string|null
@@ -46,7 +46,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -54,7 +54,6 @@ public static function xmlDeserialize(Reader $reader)
         $mixedContent = keyValue($reader);
 
         return (new static())
-            ->setId($mixedContent[Schema::CBC . 'ID'] ?? null)
-        ;
+            ->setId($mixedContent[Schema::CBC . 'ID'] ?? null);
     }
 }
diff --git a/src/Reader.php b/src/Reader.php
index 54e1d56..13de67c 100644
--- a/src/Reader.php
+++ b/src/Reader.php
@@ -6,9 +6,9 @@
 
 class Reader
 {
-    public static $currencyID;
+    public static string $currencyID;
 
-    public static function ubl($currencyId = 'EUR'): Service
+    public static function ubl(string $currencyId = 'EUR'): Service
     {
         self::$currencyID = $currencyId;
 
diff --git a/src/ReaderHelper.php b/src/ReaderHelper.php
index 8ae2eed..d382af0 100644
--- a/src/ReaderHelper.php
+++ b/src/ReaderHelper.php
@@ -12,7 +12,7 @@ class ReaderHelper
      *
      * @param string $name
      * @param ArrayCollection $collection
-     * @return ?array
+     * @return array|null
      */
     public static function getTag(string $name, ArrayCollection $collection)
     {
@@ -30,7 +30,7 @@ public static function getTag(string $name, ArrayCollection $collection)
      *
      * @param string $name
      * @param ArrayCollection $collection
-     * @return ?string
+     * @return string|null
      */
     public static function getTagValue(string $name, ArrayCollection $collection)
     {
@@ -40,11 +40,12 @@ public static function getTagValue(string $name, ArrayCollection $collection)
     }
 
     /**
-     * Get the tags with a given name from a XML Reader mixedContent result
+     * Get the tags with a given name from an XML Reader mixedContent result
      * that was converted to ArrayCollection
      *
      * @param string $name
      * @param ArrayCollection $collection
+     * @return array
      */
     public static function getArrayValue(string $name, ArrayCollection $collection)
     {
diff --git a/src/ReceiptDocumentReference.php b/src/ReceiptDocumentReference.php
index 6985984..9059ac3 100644
--- a/src/ReceiptDocumentReference.php
+++ b/src/ReceiptDocumentReference.php
@@ -17,10 +17,10 @@
  */
 class ReceiptDocumentReference implements XmlSerializable, XmlDeserializable
 {
-    private $id;
+    private ?string $id = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getId(): ?string
     {
@@ -28,7 +28,7 @@ public function getId(): ?string
     }
 
     /**
-     * @param string $id
+     * @param string|null $id
      * @return static
      */
     public function setId(?string $id)
diff --git a/src/SettlementPeriod.php b/src/SettlementPeriod.php
index d123fd5..355db15 100644
--- a/src/SettlementPeriod.php
+++ b/src/SettlementPeriod.php
@@ -26,11 +26,11 @@
  */
 class SettlementPeriod implements XmlSerializable, XmlDeserializable
 {
-    private $startDate;
-    private $endDate;
+    private ?DateTime $startDate = null;
+    private ?DateTime $endDate = null;
 
     /**
-     * @return DateTime
+     * @return DateTime|null
      */
     public function getStartDate(): ?DateTime
     {
@@ -48,7 +48,7 @@ public function setStartDate(DateTime $startDate)
     }
 
     /**
-     * @return DateTime
+     * @return DateTime|null
      */
     public function getEndDate(): ?DateTime
     {
@@ -73,8 +73,8 @@ public function setEndDate(DateTime $endDate)
      * - EndDate (BT-74): 0..1 (optional)
      * - BR-CO-19: "If Invoicing period is used, the start date or end date shall be filled, or both."
      *
-     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      * @return void
+     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      */
     public function validate()
     {
diff --git a/src/TaxCategory.php b/src/TaxCategory.php
index 7cd4130..23e9826 100644
--- a/src/TaxCategory.php
+++ b/src/TaxCategory.php
@@ -14,19 +14,19 @@
 
 class TaxCategory implements XmlSerializable, XmlDeserializable
 {
-    private $id;
-    private $idAttributes = [
+    private ?string $id = null;
+    private array $idAttributes = [
         'schemeID'   => UNCL5305::UNCL5305,
         'schemeName' => 'Duty or tax or fee category'
     ];
-    private $name;
-    private $percent;
-    private $taxScheme;
-    private $taxExemptionReason;
-    private $taxExemptionReasonCode;
+    private ?string $name = null;
+    private ?float $percent = null;
+    private ?TaxScheme $taxScheme = null;
+    private ?string $taxExemptionReason = null;
+    private ?string $taxExemptionReasonCode = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getId(): ?string
     {
@@ -45,11 +45,11 @@ public function getId(): ?string
     }
 
     /**
-     * @param string $id
-     * @param array $attributes
+     * @param string|null $id
+     * @param array|null $attributes
      * @return static
      */
-    public function setId(?string $id, $attributes = null)
+    public function setId(?string $id, array $attributes = null)
     {
         $this->id = $id;
         if (isset($attributes)) {
@@ -59,7 +59,7 @@ public function setId(?string $id, $attributes = null)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getName(): ?string
     {
@@ -67,7 +67,7 @@ public function getName(): ?string
     }
 
     /**
-     * @param string $name
+     * @param string|null $name
      * @return static
      */
     public function setName(?string $name)
@@ -77,7 +77,7 @@ public function setName(?string $name)
     }
 
     /**
-     * @return string
+     * @return float|null
      */
     public function getPercent(): ?float
     {
@@ -85,7 +85,7 @@ public function getPercent(): ?float
     }
 
     /**
-     * @param string $percent
+     * @param float|null $percent
      * @return static
      */
     public function setPercent(?float $percent)
@@ -95,7 +95,7 @@ public function setPercent(?float $percent)
     }
 
     /**
-     * @return string
+     * @return TaxScheme|null
      */
     public function getTaxScheme(): ?TaxScheme
     {
@@ -103,7 +103,7 @@ public function getTaxScheme(): ?TaxScheme
     }
 
     /**
-     * @param TaxScheme $taxScheme
+     * @param TaxScheme|null $taxScheme
      * @return static
      */
     public function setTaxScheme(?TaxScheme $taxScheme)
@@ -113,7 +113,7 @@ public function setTaxScheme(?TaxScheme $taxScheme)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getTaxExemptionReason(): ?string
     {
@@ -121,7 +121,7 @@ public function getTaxExemptionReason(): ?string
     }
 
     /**
-     * @param string $taxExemptionReason
+     * @param string|null $taxExemptionReason
      * @return static
      */
     public function setTaxExemptionReason(?string $taxExemptionReason)
@@ -131,7 +131,7 @@ public function setTaxExemptionReason(?string $taxExemptionReason)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getTaxExemptionReasonCode(): ?string
     {
@@ -139,7 +139,7 @@ public function getTaxExemptionReasonCode(): ?string
     }
 
     /**
-     * @param string $taxExemptionReason
+     * @param string|null $taxExemptionReasonCode
      * @return static
      */
     public function setTaxExemptionReasonCode(?string $taxExemptionReasonCode)
@@ -151,8 +151,8 @@ public function setTaxExemptionReasonCode(?string $taxExemptionReasonCode)
     /**
      * The validate function that is called during xml writing to valid the data of the object.
      *
-     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      * @return void
+     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      */
     public function validate()
     {
@@ -213,10 +213,9 @@ public function xmlSerialize(Writer $writer): void
     }
 
 
-
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -235,9 +234,8 @@ public static function xmlDeserialize(Reader $reader)
             ->setId($idTag['value'] ?? null, $idTag['attributes'] ?? null)
             ->setName($nameTag['value'] ?? null)
             ->setPercent(isset($percentTag['value']) ? floatval($percentTag['value']) : null)
-            ->setTaxScheme(isset($taxSchemeTag['value']) ? $taxSchemeTag['value'] : null)
+            ->setTaxScheme($taxSchemeTag['value'] ?? null)
             ->setTaxExemptionReason($taxExemptionReasonTag['value'] ?? null)
-            ->setTaxExemptionReasonCode($taxExemptionReasonCodeTag['value'] ?? null)
-        ;
+            ->setTaxExemptionReasonCode($taxExemptionReasonCodeTag['value'] ?? null);
     }
 }
diff --git a/src/TaxScheme.php b/src/TaxScheme.php
index a5d64bd..e7f191d 100644
--- a/src/TaxScheme.php
+++ b/src/TaxScheme.php
@@ -11,13 +11,13 @@
 
 class TaxScheme implements XmlSerializable, XmlDeserializable
 {
-    private $id;
-    private $name;
-    private $taxTypeCode;
-    private $currencyCode;
+    private ?string $id;
+    private ?string $name = null;
+    private ?string $taxTypeCode = null;
+    private ?string $currencyCode = null;
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getId()
     {
@@ -25,7 +25,7 @@ public function getId()
     }
 
     /**
-     * @param string $id
+     * @param string|null $id
      * @return static
      */
     public function setId(?string $id)
@@ -35,7 +35,7 @@ public function setId(?string $id)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getName(): ?string
     {
@@ -43,7 +43,7 @@ public function getName(): ?string
     }
 
     /**
-     * @param string $name
+     * @param string|null $name
      * @return static
      */
     public function setName(?string $name)
@@ -53,7 +53,7 @@ public function setName(?string $name)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getTaxTypeCode(): ?string
     {
@@ -61,7 +61,7 @@ public function getTaxTypeCode(): ?string
     }
 
     /**
-     * @param string $taxTypeCode
+     * @param string|null $taxTypeCode
      * @return static
      */
     public function setTaxTypeCode(?string $taxTypeCode)
@@ -71,7 +71,7 @@ public function setTaxTypeCode(?string $taxTypeCode)
     }
 
     /**
-     * @return string
+     * @return string|null
      */
     public function getCurrencyCode(): ?string
     {
@@ -79,7 +79,7 @@ public function getCurrencyCode(): ?string
     }
 
     /**
-     * @param string $currencyCode
+     * @param string|null $currencyCode
      * @return static
      */
     public function setCurrencyCode(?string $currencyCode)
@@ -120,7 +120,7 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
@@ -131,7 +131,6 @@ public static function xmlDeserialize(Reader $reader)
             ->setId($keyValues[Schema::CBC . 'ID'] ?? null)
             ->setName($keyValues[Schema::CBC . 'Name'] ?? null)
             ->setTaxTypeCode($keyValues[Schema::CBC . 'TaxTypeCode'] ?? null)
-            ->setCurrencyCode($keyValues[Schema::CBC . 'CurrencyCode'] ?? null)
-        ;
+            ->setCurrencyCode($keyValues[Schema::CBC . 'CurrencyCode'] ?? null);
     }
 }
diff --git a/src/TaxSubTotal.php b/src/TaxSubTotal.php
index d46fa55..fb6259d 100644
--- a/src/TaxSubTotal.php
+++ b/src/TaxSubTotal.php
@@ -13,13 +13,13 @@
 
 class TaxSubTotal implements XmlSerializable, XmlDeserializable
 {
-    private $taxableAmount;
-    private $taxAmount;
-    private $taxCategory;
-    private $percent;
+    private ?float $taxableAmount = null;
+    private ?float $taxAmount = null;
+    private ?TaxCategory $taxCategory = null;
+    private ?float $percent = null;
 
     /**
-     * @return mixed
+     * @return float|null
      */
     public function getTaxableAmount(): ?float
     {
@@ -27,7 +27,7 @@ public function getTaxableAmount(): ?float
     }
 
     /**
-     * @param mixed $taxableAmount
+     * @param float|null $taxableAmount
      * @return static
      */
     public function setTaxableAmount(?float $taxableAmount)
@@ -37,7 +37,7 @@ public function setTaxableAmount(?float $taxableAmount)
     }
 
     /**
-     * @return mixed
+     * @return float|null
      */
     public function getTaxAmount(): ?float
     {
@@ -45,7 +45,7 @@ public function getTaxAmount(): ?float
     }
 
     /**
-     * @param mixed $taxAmount
+     * @param float|null $taxAmount
      * @return static
      */
     public function setTaxAmount(?float $taxAmount)
@@ -55,7 +55,7 @@ public function setTaxAmount(?float $taxAmount)
     }
 
     /**
-     * @return TaxCategory
+     * @return TaxCategory|null
      */
     public function getTaxCategory(): ?TaxCategory
     {
@@ -63,7 +63,7 @@ public function getTaxCategory(): ?TaxCategory
     }
 
     /**
-     * @param TaxCategory $taxCategory
+     * @param TaxCategory|null $taxCategory
      * @return static
      */
     public function setTaxCategory(?TaxCategory $taxCategory)
@@ -73,7 +73,7 @@ public function setTaxCategory(?TaxCategory $taxCategory)
     }
 
     /**
-     * @return float
+     * @return float|null
      */
     public function getPercent(): ?float
     {
@@ -81,7 +81,7 @@ public function getPercent(): ?float
     }
 
     /**
-     * @param float $percent
+     * @param float|null $percent
      * @return static
      */
     public function setPercent(?float $percent)
@@ -93,8 +93,8 @@ public function setPercent(?float $percent)
     /**
      * The validate function that is called during xml writing to valid the data of the object.
      *
-     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      * @return void
+     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      */
     public function validate()
     {
@@ -150,18 +150,27 @@ public function xmlSerialize(Writer $writer): void
 
     /**
      * The xmlDeserialize method is called during xml reading.
-     * @param Reader $xml
+     * @param Reader $reader
      * @return static
      */
     public static function xmlDeserialize(Reader $reader)
     {
         $keyValues = keyValue($reader);
 
+        $taxableAmount = isset($keyValues[Schema::CBC . 'TaxableAmount'])
+            ? floatval($keyValues[Schema::CBC . 'TaxableAmount'])
+            : null;
+
+        $taxAmount = isset($keyValues[Schema::CBC . 'TaxAmount'])
+            ? floatval($keyValues[Schema::CBC . 'TaxAmount'])
+            : null;
+
+        $percent = isset($keyValues[Schema::CBC . 'Percent']) ? floatval($keyValues[Schema::CBC . 'Percent']) : null;
+
         return (new static())
-            ->setTaxableAmount(isset($keyValues[Schema::CBC . 'TaxableAmount']) ? floatval($keyValues[Schema::CBC . 'TaxableAmount']) : null)
-            ->setTaxAmount(isset($keyValues[Schema::CBC . 'TaxAmount']) ? floatval($keyValues[Schema::CBC . 'TaxAmount']) : null)
+            ->setTaxableAmount($taxableAmount)
+            ->setTaxAmount($taxAmount)
             ->setTaxCategory($keyValues[Schema::CAC . 'TaxCategory'] ?? null)
-            ->setPercent(isset($keyValues[Schema::CBC . 'Percent']) ? floatval($keyValues[Schema::CBC . 'Percent']) : null)
-        ;
+            ->setPercent($percent);
     }
 }
diff --git a/src/TaxTotal.php b/src/TaxTotal.php
index 3abf236..96692b8 100644
--- a/src/TaxTotal.php
+++ b/src/TaxTotal.php
@@ -14,11 +14,11 @@
 
 class TaxTotal implements XmlSerializable, XmlDeserializable
 {
-    private $taxAmount;
-    private $taxSubTotals = [];
+    private ?float $taxAmount = null;
+    private array $taxSubTotals = [];
 
     /**
-     * @return mixed
+     * @return float|null
      */
     public function getTaxAmount(): ?float
     {
@@ -26,7 +26,7 @@ public function getTaxAmount(): ?float
     }
 
     /**
-     * @param mixed $taxAmount
+     * @param float|null $taxAmount
      * @return static
      */
     public function setTaxAmount(?float $taxAmount)
@@ -44,7 +44,7 @@ public function getTaxSubTotals(): array
     }
 
     /**
-     * @param array<TaxSubTotal> $taxSubTotal
+     * @param array $taxSubTotals
      * @return static
      */
     public function setTaxSubTotals(array $taxSubTotals)
@@ -66,8 +66,8 @@ public function addTaxSubTotal(TaxSubTotal $taxSubTotal)
     /**
      * The validate function that is called during xml writing to valid the data of the object.
      *
-     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      * @return void
+     * @throws InvalidArgumentException An error with information about required data that is missing to write the XML
      */
     public function validate()
     {
diff --git a/tests/NumberFormatterTest.php b/tests/NumberFormatterTest.php
index c195c12..d4ad944 100644
--- a/tests/NumberFormatterTest.php
+++ b/tests/NumberFormatterTest.php
@@ -16,7 +16,7 @@ class NumberFormatterTest extends TestCase
     public function testNumberFormatterRounding($number, string $formattedNumber, ?int $decimals)
     {
         $result = NumberFormatter::format($number, $decimals);
-        return $this->assertEqualsCanonicalizing($formattedNumber, $result);
+        $this->assertEqualsCanonicalizing($formattedNumber, $result);
     }
 
     public function formattedNumbersProvider(): array
diff --git a/tests/Read/AddressLineTest.php b/tests/Read/AddressLineTest.php
index 3ffa3b6..6139daa 100644
--- a/tests/Read/AddressLineTest.php
+++ b/tests/Read/AddressLineTest.php
@@ -5,6 +5,7 @@
 use NumNum\UBL\Address;
 use NumNum\UBL\AddressLine;
 use NumNum\UBL\Invoice;
+use NumNum\UBL\Reader;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -70,7 +71,7 @@ public function testAddressLineDeserializesFromXml()
 </Invoice>
 XML;
 
-        $ublReader = \NumNum\UBL\Reader::ubl();
+        $ublReader = Reader::ubl();
         $invoice = $ublReader->parse($xml);
 
         $this->assertInstanceOf(Invoice::class, $invoice);
@@ -156,7 +157,7 @@ public function testSingleAddressLineDeserializes()
 </Invoice>
 XML;
 
-        $ublReader = \NumNum\UBL\Reader::ubl();
+        $ublReader = Reader::ubl();
         $invoice = $ublReader->parse($xml);
 
         $address = $invoice->getAccountingSupplierParty()->getParty()->getPostalAddress();
@@ -166,4 +167,3 @@ public function testSingleAddressLineDeserializes()
         $this->assertEquals('Only One Line', $addressLines[0]->getLine());
     }
 }
-
diff --git a/tests/Read/DespatchDocumentReferenceTest.php b/tests/Read/DespatchDocumentReferenceTest.php
index 1819214..5a250dc 100644
--- a/tests/Read/DespatchDocumentReferenceTest.php
+++ b/tests/Read/DespatchDocumentReferenceTest.php
@@ -26,4 +26,3 @@ public function testDespatchDocumentReferenceCanBeRead()
         $this->assertEquals('DESP-2024-001', $despatchDocumentReference->getId());
     }
 }
-
diff --git a/tests/Read/ItemOriginCountryTest.php b/tests/Read/ItemOriginCountryTest.php
index 7f0d19a..9decf05 100644
--- a/tests/Read/ItemOriginCountryTest.php
+++ b/tests/Read/ItemOriginCountryTest.php
@@ -4,6 +4,7 @@
 
 use NumNum\UBL\Country;
 use NumNum\UBL\Invoice;
+use NumNum\UBL\Reader;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -55,7 +56,7 @@ public function testItemOriginCountryCanBeRead()
 </Invoice>
 XML;
 
-        $ublReader = \NumNum\UBL\Reader::ubl();
+        $ublReader = Reader::ubl();
         $invoice = $ublReader->parse($xml);
 
         $this->assertNotNull($invoice);
@@ -115,7 +116,7 @@ public function testItemWithoutOriginCountryCanBeRead()
 </Invoice>
 XML;
 
-        $ublReader = \NumNum\UBL\Reader::ubl();
+        $ublReader = Reader::ubl();
         $invoice = $ublReader->parse($xml);
 
         $this->assertNotNull($invoice);
@@ -133,4 +134,3 @@ public function testItemWithoutOriginCountryCanBeRead()
         $this->assertNull($originCountry);
     }
 }
-
diff --git a/tests/Read/PayeePartyTest.php b/tests/Read/PayeePartyTest.php
index d8896a1..fc64e8c 100644
--- a/tests/Read/PayeePartyTest.php
+++ b/tests/Read/PayeePartyTest.php
@@ -4,6 +4,7 @@
 
 use NumNum\UBL\Invoice;
 use NumNum\UBL\PayeeParty;
+use NumNum\UBL\Reader;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -80,7 +81,7 @@ public function testPayeePartyDeserializesFromXml()
 </Invoice>
 XML;
 
-        $ublReader = \NumNum\UBL\Reader::ubl();
+        $ublReader = Reader::ubl();
         $invoice = $ublReader->parse($xml);
 
         $this->assertInstanceOf(Invoice::class, $invoice);
diff --git a/tests/Read/ReadUbl.php b/tests/Read/ReadUbl.php
index f8c2f71..e3cff0a 100644
--- a/tests/Read/ReadUbl.php
+++ b/tests/Read/ReadUbl.php
@@ -4,6 +4,7 @@
 
 use NumNum\UBL\CreditNote;
 use NumNum\UBL\Invoice;
+use NumNum\UBL\Reader;
 use PHPUnit\Framework\TestCase;
 
 class ReadUbl extends TestCase
@@ -14,7 +15,7 @@ class ReadUbl extends TestCase
      */
     public function testIfInvoiceUblCanBeRead($fileName)
     {
-        $ublReader = \NumNum\UBL\Reader::ubl();
+        $ublReader = Reader::ubl();
 
         $invoice = $ublReader->parse(file_get_contents($fileName));
 
@@ -28,7 +29,7 @@ public function testIfInvoiceUblCanBeRead($fileName)
      */
     public function testIfCreditNoteUblCanBeRead($fileName)
     {
-        $ublReader = \NumNum\UBL\Reader::ubl();
+        $ublReader = Reader::ubl();
 
         $invoice = $ublReader->parse(file_get_contents($fileName));
 
diff --git a/tests/Read/TaxTotalTest.php b/tests/Read/TaxTotalTest.php
index 1e1fb79..1a3a711 100644
--- a/tests/Read/TaxTotalTest.php
+++ b/tests/Read/TaxTotalTest.php
@@ -132,4 +132,3 @@ public function testSingleTaxTotalDeserializes()
         $this->assertEquals(21, $taxCategory->getPercent());
     }
 }
-
diff --git a/tests/Write/AddressLineTest.php b/tests/Write/AddressLineTest.php
index dfbb08c..e9114f4 100644
--- a/tests/Write/AddressLineTest.php
+++ b/tests/Write/AddressLineTest.php
@@ -2,6 +2,8 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
 use NumNum\UBL\Address;
 use NumNum\UBL\AddressLine;
 use NumNum\UBL\Country;
@@ -25,7 +27,7 @@
  */
 class AddressLineTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
 
     /** @test */
     public function testAddressLineSerializesToXml()
@@ -112,7 +114,7 @@ public function testAddressLineSerializesToXml()
         $invoice = (new Invoice())
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -129,7 +131,7 @@ public function testAddressLineSerializesToXml()
         $this->assertStringContainsString('<cbc:Line>Suite 5</cbc:Line>', $outputXMLString);
 
         // Create PHP Native DomDocument object for validation
-        $dom = new \DOMDocument();
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $this->assertEquals(true, $dom->schemaValidate($this->schema));
@@ -220,7 +222,7 @@ public function testAddressWithoutAddressLinesIsValid()
         $invoice = (new Invoice())
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -235,7 +237,7 @@ public function testAddressWithoutAddressLinesIsValid()
         $this->assertStringNotContainsString('<cac:AddressLine>', $outputXMLString);
 
         // Create PHP Native DomDocument object for validation
-        $dom = new \DOMDocument();
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $this->assertEquals(true, $dom->schemaValidate($this->schema));
@@ -259,4 +261,3 @@ public function testSetAddressLinesReplacesExisting()
         $this->assertEquals('New Line', $address->getAddressLines()[0]->getLine());
     }
 }
-
diff --git a/tests/Write/BillingReferenceCreditNoteTest.php b/tests/Write/BillingReferenceCreditNoteTest.php
index 63f6e10..2674634 100644
--- a/tests/Write/BillingReferenceCreditNoteTest.php
+++ b/tests/Write/BillingReferenceCreditNoteTest.php
@@ -2,6 +2,26 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\BillingReference;
+use NumNum\UBL\Country;
+use NumNum\UBL\CreditNote;
+use NumNum\UBL\CreditNoteLine;
+use NumNum\UBL\Generator;
+use NumNum\UBL\InvoiceDocumentReference;
+use NumNum\UBL\InvoiceTypeCode;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +29,17 @@
  */
 class BillingReferenceCreditNoteTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-CreditNote-2.1.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-CreditNote-2.1.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,43 +47,43 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description')
             ->setSellersItemIdentification('SELLERID')
             ->setBuyersItemIdentification('BUYERID');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // Invoice Line(s)
-        $creditNoteLine = (new \NumNum\UBL\CreditNoteLine())
+        $creditNoteLine = (new CreditNoteLine())
             ->setId(0)
             ->setItem($productItem)
             ->setPrice($price)
@@ -73,53 +93,53 @@ public function testIfXMLIsValid()
         $creditNoteLines = [$creditNoteLine];
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
-        $billingReference = (new \NumNum\UBL\BillingReference())
-            ->setInvoiceDocumentReference((new \NumNum\UBL\InvoiceDocumentReference())
+        $billingReference = (new BillingReference())
+            ->setInvoiceDocumentReference((new InvoiceDocumentReference())
                     ->setOriginalInvoiceId(1234)
-                    ->setIssueDate(new \DateTime()));
+                    ->setIssueDate(new DateTime()));
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setParty($clientCompany);
 
         // Invoice object
-        $creditNote = (new \NumNum\UBL\CreditNote())
+        $creditNote = (new CreditNote())
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setBillingReference($billingReference)
             ->setCreditNoteLines($creditNoteLines)
             ->setLegalMonetaryTotal($legalMonetaryTotal)
             ->setTaxTotal($taxTotal)
-            ->setInvoiceTypeCode(\NumNum\UBL\InvoiceTypeCode::CREDIT_NOTE);
+            ->setInvoiceTypeCode(InvoiceTypeCode::CREDIT_NOTE);
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->creditNote($creditNote);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/BillingReferenceTest.xml');
diff --git a/tests/Write/ContractDocumentReferenceTest.php b/tests/Write/ContractDocumentReferenceTest.php
index c41a090..ba9a59e 100644
--- a/tests/Write/ContractDocumentReferenceTest.php
+++ b/tests/Write/ContractDocumentReferenceTest.php
@@ -2,6 +2,26 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\ContractDocumentReference;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoicePeriod;
+use NumNum\UBL\InvoiceTypeCode;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +29,17 @@
  */
 class ContractDocumentReferenceTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,41 +47,41 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // Invoice Line(s)
-        $invoiceLine = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLine = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setPrice($price)
@@ -71,42 +91,42 @@ public function testIfXMLIsValid()
         $invoiceLines = [$invoiceLine];
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
-        $contractDocumentReference = (new \NumNum\UBL\ContractDocumentReference())
+        $contractDocumentReference = (new ContractDocumentReference())
             ->setId("123Test");
 
-        $invoicePeriod = (new \NumNum\UBL\InvoicePeriod())
-            ->setStartDate(new \DateTime('-31 days'))
-            ->setEndDate(new \DateTime());
+        $invoicePeriod = (new InvoicePeriod())
+            ->setStartDate(new DateTime('-31 days'))
+            ->setEndDate(new DateTime());
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setUBLVersionId('2.2')
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
-            ->setInvoiceTypeCode(\NumNum\UBL\InvoiceTypeCode::INVOICE)
-            ->setDueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
+            ->setInvoiceTypeCode(InvoiceTypeCode::INVOICE)
+            ->setDueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -118,12 +138,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/ContractDocumentReferenceTest.xml');
diff --git a/tests/Write/DespatchDocumentReferenceTest.php b/tests/Write/DespatchDocumentReferenceTest.php
index 93d392c..f18906d 100644
--- a/tests/Write/DespatchDocumentReferenceTest.php
+++ b/tests/Write/DespatchDocumentReferenceTest.php
@@ -2,6 +2,25 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\Country;
+use NumNum\UBL\DespatchDocumentReference;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoiceTypeCode;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +28,17 @@
  */
 class DespatchDocumentReferenceTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,41 +46,41 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // Invoice Line(s)
-        $invoiceLine = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLine = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setPrice($price)
@@ -71,38 +90,38 @@ public function testIfXMLIsValid()
         $invoiceLines = [$invoiceLine];
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
-        $despatchDocumentReference = (new \NumNum\UBL\DespatchDocumentReference())
+        $despatchDocumentReference = (new DespatchDocumentReference())
             ->setId("DESP-2024-001");
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setUBLVersionId('2.2')
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
-            ->setInvoiceTypeCode(\NumNum\UBL\InvoiceTypeCode::INVOICE)
-            ->setDueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
+            ->setInvoiceTypeCode(InvoiceTypeCode::INVOICE)
+            ->setDueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -113,12 +132,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $this->assertEquals(true, $dom->schemaValidate($this->schema));
@@ -128,11 +147,11 @@ public function testIfXMLIsValid()
     public function testDespatchDocumentReferenceIsInOutput()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -140,59 +159,58 @@ public function testDespatchDocumentReferenceIsInOutput()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPostalAddress($address);
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(12);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line(s)
-        $invoiceLine = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLine = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setPrice($price)
             ->setInvoicedQuantity(1);
 
-        $despatchDocumentReference = (new \NumNum\UBL\DespatchDocumentReference())
+        $despatchDocumentReference = (new DespatchDocumentReference())
             ->setId("DESP-2024-001");
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setId(1234)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines([$invoiceLine])
             ->setLegalMonetaryTotal($legalMonetaryTotal)
             ->setDespatchDocumentReference($despatchDocumentReference);
 
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         $this->assertStringContainsString('<cac:DespatchDocumentReference>', $outputXMLString);
         $this->assertStringContainsString('<cbc:ID>DESP-2024-001</cbc:ID>', $outputXMLString);
     }
 }
-
diff --git a/tests/Write/DocumentTypeTest.php b/tests/Write/DocumentTypeTest.php
index 7d3657d..f56d34d 100644
--- a/tests/Write/DocumentTypeTest.php
+++ b/tests/Write/DocumentTypeTest.php
@@ -2,6 +2,27 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\AdditionalDocumentReference;
+use NumNum\UBL\Address;
+use NumNum\UBL\Attachment;
+use NumNum\UBL\Contact;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoicePeriod;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +30,17 @@
  */
 class DocumentTypeTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,56 +48,56 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client contact node
-        $clientContact = (new \NumNum\UBL\Contact())
+        $clientContact = (new Contact())
             ->setName('Client name')
             ->setElectronicMail('email@client.com')
             ->setTelephone('0032 472 123 456')
             ->setTelefax('0032 9 1234 567');
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address)
             ->setContact($clientContact);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description')
             ->setSellersItemIdentification('SELLERID');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // InvoicePeriod
-        $invoicePeriod = (new \NumNum\UBL\InvoicePeriod())
-            ->setStartDate(new \DateTime());
+        $invoicePeriod = (new InvoicePeriod())
+            ->setStartDate(new DateTime());
 
         // Invoice Line(s)
         $invoiceLines = [];
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -84,7 +105,7 @@ public function testIfXMLIsValid()
             ->setTaxTotal($lineTaxTotal)
             ->setInvoicedQuantity(1);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -93,7 +114,7 @@ public function testIfXMLIsValid()
             ->setTaxTotal($lineTaxTotal)
             ->setInvoicedQuantity(1);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -104,42 +125,49 @@ public function testIfXMLIsValid()
 
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
         // Attachment
-        $attachment = (new \NumNum\UBL\Attachment())
-            ->setFilePath(__DIR__.DIRECTORY_SEPARATOR.'..'.DIRECTORY_SEPARATOR.'Files'.DIRECTORY_SEPARATOR.'SampleInvoice.pdf');
-
-        $additionalDocumentReference = new \NumNum\UBL\AdditionalDocumentReference();
+        $attachment_filepath = __DIR__
+            .DIRECTORY_SEPARATOR
+            .'..'
+            .DIRECTORY_SEPARATOR
+            .'Files'
+            .DIRECTORY_SEPARATOR
+            .'SampleInvoice.pdf';
+        $attachment = (new Attachment())
+            ->setFilePath($attachment_filepath);
+
+        $additionalDocumentReference = new AdditionalDocumentReference();
         $additionalDocumentReference->setId('SomeID');
         $additionalDocumentReference->setDocumentType("CommercialInvoice");
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setSupplierAssignedAccountId('10001')
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -149,12 +177,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/EmptyAttachmentTest.xml');
diff --git a/tests/Write/DueDateTest.php b/tests/Write/DueDateTest.php
index 559a478..7a07ccb 100644
--- a/tests/Write/DueDateTest.php
+++ b/tests/Write/DueDateTest.php
@@ -2,6 +2,24 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoiceTypeCode;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +27,17 @@
  */
 class DueDateTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,41 +45,41 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // Invoice Line(s)
-        $invoiceLine = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLine = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setPrice($price)
@@ -71,35 +89,35 @@ public function testIfXMLIsValid()
         $invoiceLines = [$invoiceLine];
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setUBLVersionId('2.2')
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
-            ->setInvoiceTypeCode(\NumNum\UBL\InvoiceTypeCode::INVOICE)
-            ->setDueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
+            ->setInvoiceTypeCode(InvoiceTypeCode::INVOICE)
+            ->setDueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -108,12 +126,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/DueDateTest.xml');
diff --git a/tests/Write/EN16931Test.php b/tests/Write/EN16931Test.php
index 1b8e82a..9b000b0 100644
--- a/tests/Write/EN16931Test.php
+++ b/tests/Write/EN16931Test.php
@@ -2,59 +2,84 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\ClassifiedTaxCategory;
+use NumNum\UBL\Country;
+use NumNum\UBL\Delivery;
+use NumNum\UBL\FinancialInstitutionBranch;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoicePeriod;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalEntity;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\OrderReference;
+use NumNum\UBL\Party;
+use NumNum\UBL\PartyTaxScheme;
+use NumNum\UBL\PayeeFinancialAccount;
+use NumNum\UBL\PaymentMeans;
+use NumNum\UBL\PaymentTerms;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
 use NumNum\UBL\UNCL4461;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
+use SoapClient;
 
 /**
  * Test an UBL2.1 invoice document
  */
 class EN16931Test extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
-    private $xslfile = 'vendor/num-num/ubl-invoice/tests/EN16931-UBL-validation.xslt';
-
     /** @test */
     public function testIfXMLIsValid()
     {
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId('VAT');
 
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt 1')
             ->setAdditionalStreetName('Building A')
             ->setCityName('Gent')
             ->setPostalZone('9000')
             ->setCountry($country);
 
-        $financialInstitutionBranch = (new \NumNum\UBL\FinancialInstitutionBranch())
+        $financialInstitutionBranch = (new FinancialInstitutionBranch())
             ->setId('RABONL2U');
 
-        $payeeFinancialAccount = (new \NumNum\UBL\PayeeFinancialAccount())
+        $payeeFinancialAccount = (new PayeeFinancialAccount())
            ->setFinancialInstitutionBranch($financialInstitutionBranch)
             ->setName('Customer Account Holder')
             ->setId('NL00RABO0000000000');
 
-        $paymentMeans = (new \NumNum\UBL\PaymentMeans())
+        $paymentMeans = (new PaymentMeans())
             ->setPayeeFinancialAccount($payeeFinancialAccount)
             ->setPaymentMeansCode(UNCL4461::DEBIT_TRANSFER, [])
             ->setPaymentId('our invoice 1234');
 
         // Supplier company node
-        $supplierLegalEntity = (new \NumNum\UBL\LegalEntity())
+        $supplierLegalEntity = (new LegalEntity())
             ->setRegistrationName('Supplier Company Name')
             ->setCompanyId('BE123456789');
 
-        $supplierPartyTaxScheme = (new \NumNum\UBL\PartyTaxScheme())
+        $supplierPartyTaxScheme = (new PartyTaxScheme())
             ->setTaxScheme($taxScheme)
             ->setCompanyId('BE123456789');
 
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setLegalEntity($supplierLegalEntity)
             ->setPartyTaxScheme($supplierPartyTaxScheme)
@@ -62,55 +87,55 @@ public function testIfXMLIsValid()
             ->setPostalAddress($address);
 
         // Client company node
-        $clientLegalEntity = (new \NumNum\UBL\LegalEntity())
+        $clientLegalEntity = (new LegalEntity())
             ->setRegistrationName('Client Company Name')
             ->setCompanyId('Client Company Registration');
 
-        $clientPartyTaxScheme = (new \NumNum\UBL\PartyTaxScheme())
+        $clientPartyTaxScheme = (new PartyTaxScheme())
             ->setTaxScheme($taxScheme)
             ->setCompanyId('BE123456789');
 
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('Client Company Name')
             ->setLegalEntity($clientLegalEntity)
             ->setPartyTaxScheme($clientPartyTaxScheme)
             ->setPartyIdentificationId('BE123456789')
             ->setPostalAddress($address);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2.1)
             ->setPayableRoundingAmount(0)
             ->setTaxInclusiveAmount(10 + 2.1)
             ->setLineExtensionAmount(10)
             ->setTaxExclusiveAmount(10);
 
-        $classifiedTaxCategory = (new \NumNum\UBL\ClassifiedTaxCategory())
+        $classifiedTaxCategory = (new ClassifiedTaxCategory())
             ->setId('S')
             ->setPercent(21.00)
             ->setTaxScheme($taxScheme);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setClassifiedTaxCategory($classifiedTaxCategory)
             ->setDescription('Product Description');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // InvoicePeriod
-        $invoicePeriod = (new \NumNum\UBL\InvoicePeriod())
-            ->setStartDate(new \DateTime());
+        $invoicePeriod = (new InvoicePeriod())
+            ->setStartDate(new DateTime());
 
         // Invoice Line(s)
-        $invoiceLine = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLine = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setPrice($price)
@@ -121,48 +146,48 @@ public function testIfXMLIsValid()
         $invoiceLines = [$invoiceLine];
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId('S', [])
             ->setPercent(21.00)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
         // Payment Terms
-        $paymentTerms = (new \NumNum\UBL\PaymentTerms())
+        $paymentTerms = (new PaymentTerms())
             ->setNote('30 days net');
 
         // Delivery
-        $deliveryLocation = (new \NumNum\UBL\Address())
+        $deliveryLocation = (new Address())
             ->setCountry($country);
 
-        $delivery = (new \NumNum\UBL\Delivery())
-            ->setActualDeliveryDate(new \DateTime())
+        $delivery = (new Delivery())
+            ->setActualDeliveryDate(new DateTime())
             ->setDeliveryLocation($deliveryLocation);
 
-        $orderReference = (new \NumNum\UBL\OrderReference())
+        $orderReference = (new OrderReference())
             ->setId('5009567')
             ->setSalesOrderId('tRST-tKhM');
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setCustomizationId('urn:cen.eu:en16931:2017')
             ->setId(1234)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setNote('invoice note')
             ->setDelivery($delivery)
             ->setAccountingSupplierParty($accountingSupplierParty)
@@ -178,21 +203,19 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/EN16931Test.xml');
 
-        // $this->assertEquals(true, $dom->schemaValidate($this->schema));
-
         // Use webservice at peppol.helger.com to verify the result
         $wsdl = "http://peppol.helger.com/wsdvs?wsdl=1";
-        $client = new \SoapClient($wsdl);
+        $client = new SoapClient($wsdl);
         $response = $client->validate(['XML' => $outputXMLString, 'VESID' => 'eu.cen.en16931:ubl:1.3.1']);
 
         // Output validation warnings if present
diff --git a/tests/Write/EmptyAttachmentTest.php b/tests/Write/EmptyAttachmentTest.php
index 9f95284..bc5745b 100644
--- a/tests/Write/EmptyAttachmentTest.php
+++ b/tests/Write/EmptyAttachmentTest.php
@@ -2,6 +2,27 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\AdditionalDocumentReference;
+use NumNum\UBL\Address;
+use NumNum\UBL\Attachment;
+use NumNum\UBL\Contact;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoicePeriod;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +30,17 @@
  */
 class EmptyAttachmentTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,56 +48,56 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client contact node
-        $clientContact = (new \NumNum\UBL\Contact())
+        $clientContact = (new Contact())
             ->setName('Client name')
             ->setElectronicMail('email@client.com')
             ->setTelephone('0032 472 123 456')
             ->setTelefax('0032 9 1234 567');
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address)
             ->setContact($clientContact);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description')
             ->setSellersItemIdentification('SELLERID');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // InvoicePeriod
-        $invoicePeriod = (new \NumNum\UBL\InvoicePeriod())
-            ->setStartDate(new \DateTime());
+        $invoicePeriod = (new InvoicePeriod())
+            ->setStartDate(new DateTime());
 
         // Invoice Line(s)
         $invoiceLines = [];
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -84,7 +105,7 @@ public function testIfXMLIsValid()
             ->setTaxTotal($lineTaxTotal)
             ->setInvoicedQuantity(1);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -93,7 +114,7 @@ public function testIfXMLIsValid()
             ->setTaxTotal($lineTaxTotal)
             ->setInvoicedQuantity(1);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -104,45 +125,52 @@ public function testIfXMLIsValid()
 
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
         // Attachment
-        $attachment = (new \NumNum\UBL\Attachment())
-            ->setFilePath(__DIR__.DIRECTORY_SEPARATOR.'..'.DIRECTORY_SEPARATOR.'Files'.DIRECTORY_SEPARATOR.'SampleInvoice.pdf');
-
-        $additionalDocumentReference = new \NumNum\UBL\AdditionalDocumentReference();
+        $attachment_filepath = __DIR__
+            .DIRECTORY_SEPARATOR
+            .'..'
+            .DIRECTORY_SEPARATOR
+            .'Files'
+            .DIRECTORY_SEPARATOR
+            .'SampleInvoice.pdf';
+        $attachment = (new Attachment())
+            ->setFilePath($attachment_filepath);
+
+        $additionalDocumentReference = new AdditionalDocumentReference();
         $additionalDocumentReference->setId('SomeID');
         $additionalDocumentReference->setDocumentTypeCode(130);
 
         // Not adding an attachment to AdditionalDocumentReference should not trigger an error
         // $additionalDocumentReference->setAttachment($attachment);
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setSupplierAssignedAccountId('10001')
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -152,12 +180,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/EmptyAttachmentTest.xml');
diff --git a/tests/Write/ExternalReferenceOnlyAttachmentTest.php b/tests/Write/ExternalReferenceOnlyAttachmentTest.php
index 0e2e839..50a5c4f 100644
--- a/tests/Write/ExternalReferenceOnlyAttachmentTest.php
+++ b/tests/Write/ExternalReferenceOnlyAttachmentTest.php
@@ -2,6 +2,27 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\AdditionalDocumentReference;
+use NumNum\UBL\Address;
+use NumNum\UBL\Attachment;
+use NumNum\UBL\Contact;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoicePeriod;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +30,17 @@
  */
 class ExternalReferenceOnlyAttachmentTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,56 +48,56 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client contact node
-        $clientContact = (new \NumNum\UBL\Contact())
+        $clientContact = (new Contact())
             ->setName('Client name')
             ->setElectronicMail('email@client.com')
             ->setTelephone('0032 472 123 456')
             ->setTelefax('0032 9 1234 567');
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address)
             ->setContact($clientContact);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description')
             ->setSellersItemIdentification('SELLERID');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // InvoicePeriod
-        $invoicePeriod = (new \NumNum\UBL\InvoicePeriod())
-            ->setStartDate(new \DateTime());
+        $invoicePeriod = (new InvoicePeriod())
+            ->setStartDate(new DateTime());
 
         // Invoice Line(s)
         $invoiceLines = [];
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -85,42 +106,42 @@ public function testIfXMLIsValid()
             ->setInvoicedQuantity(1);
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
         // Attachment with only external reference (no embedded binary object)
-        $attachment = (new \NumNum\UBL\Attachment())
+        $attachment = (new Attachment())
             ->setExternalReference('https://payment.quickpay.net/payments/abc123');
 
-        $additionalDocumentReference = (new \NumNum\UBL\AdditionalDocumentReference())
+        $additionalDocumentReference = (new AdditionalDocumentReference())
             ->setId('PaymentLink')
             ->setDocumentDescription('Payment link for invoice')
             ->setAttachment($attachment);
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setSupplierAssignedAccountId('10001')
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -130,12 +151,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/ExternalReferenceOnlyAttachmentTest.xml');
@@ -147,57 +168,57 @@ public function testIfXMLIsValid()
     public function testExternalReferenceOnlyDoesNotContainEmbeddedDocument()
     {
         // Attachment with only external reference (no embedded binary object)
-        $attachment = (new \NumNum\UBL\Attachment())
+        $attachment = (new Attachment())
             ->setExternalReference('https://payment.quickpay.net/payments/abc123');
 
-        $additionalDocumentReference = (new \NumNum\UBL\AdditionalDocumentReference())
+        $additionalDocumentReference = (new AdditionalDocumentReference())
             ->setId('PaymentLink')
             ->setAttachment($attachment);
 
         // Generate just the AdditionalDocumentReference XML
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
 
         // Create a minimal invoice to test the attachment serialization
-        $country = (new \NumNum\UBL\Country())->setIdentificationCode('BE');
-        $address = (new \NumNum\UBL\Address())
+        $country = (new Country())->setIdentificationCode('BE');
+        $address = (new Address())
             ->setStreetName('Test')
             ->setCityName('Test')
             ->setCountry($country);
 
-        $party = (new \NumNum\UBL\Party())
+        $party = (new Party())
             ->setName('Test')
             ->setPostalAddress($address);
 
-        $accountingParty = (new \NumNum\UBL\AccountingParty())
+        $accountingParty = (new AccountingParty())
             ->setParty($party);
 
-        $taxScheme = (new \NumNum\UBL\TaxScheme())->setId(0);
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxScheme = (new TaxScheme())->setId(0);
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setPercent(0)
             ->setTaxScheme($taxScheme);
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(0)
             ->setTaxAmount(0)
             ->setTaxCategory($taxCategory);
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(0);
 
-        $item = (new \NumNum\UBL\Item())->setName('Test');
-        $price = (new \NumNum\UBL\Price())->setPriceAmount(0);
-        $invoiceLine = (new \NumNum\UBL\InvoiceLine())
+        $item = (new Item())->setName('Test');
+        $price = (new Price())->setPriceAmount(0);
+        $invoiceLine = (new InvoiceLine())
             ->setId(1)
             ->setItem($item)
             ->setPrice($price)
             ->setInvoicedQuantity(1);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(0);
 
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setId(1)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingParty)
             ->setAccountingCustomerParty($accountingParty)
             ->setInvoiceLines([$invoiceLine])
@@ -218,4 +239,3 @@ public function testExternalReferenceOnlyDoesNotContainEmbeddedDocument()
         $this->assertStringNotContainsString('EmbeddedDocumentBinaryObject', $outputXMLString);
     }
 }
-
diff --git a/tests/Write/ItemOriginCountryTest.php b/tests/Write/ItemOriginCountryTest.php
index b6f4cd4..5c07bcc 100644
--- a/tests/Write/ItemOriginCountryTest.php
+++ b/tests/Write/ItemOriginCountryTest.php
@@ -2,6 +2,23 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +26,17 @@
  */
 class ItemOriginCountryTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
 
     /** @test */
     public function testItemWithOriginCountryIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,49 +44,49 @@ public function testItemWithOriginCountryIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Origin country for the product
-        $originCountry = (new \NumNum\UBL\Country())
+        $originCountry = (new Country())
             ->setIdentificationCode('CN');
 
         // Product with OriginCountry
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description')
             ->setSellersItemIdentification('SELLERID')
             ->setOriginCountry($originCountry);
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // Invoice Line(s)
         $invoiceLines = [];
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setPrice($price)
@@ -77,33 +94,33 @@ public function testItemWithOriginCountryIsValid()
             ->setInvoicedQuantity(1);
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setSupplierAssignedAccountId('10001')
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -112,7 +129,7 @@ public function testItemWithOriginCountryIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Verify that the OriginCountry element is present in the XML
@@ -121,7 +138,7 @@ public function testItemWithOriginCountryIsValid()
 
         // Create PHP Native DomDocument object, that can be
         // used to validate the generated XML
-        $dom = new \DOMDocument();
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/ItemOriginCountryTest.xml');
@@ -129,4 +146,3 @@ public function testItemWithOriginCountryIsValid()
         $this->assertEquals(true, $dom->schemaValidate($this->schema));
     }
 }
-
diff --git a/tests/Write/MultiplePaymentMeansTest.php b/tests/Write/MultiplePaymentMeansTest.php
index 7a32819..99cd58f 100644
--- a/tests/Write/MultiplePaymentMeansTest.php
+++ b/tests/Write/MultiplePaymentMeansTest.php
@@ -2,6 +2,28 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\CommodityClassification;
+use NumNum\UBL\Contact;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoicePeriod;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\PayeeFinancialAccount;
+use NumNum\UBL\PaymentMeans;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +31,17 @@
  */
 class MultiplePaymentMeansTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,39 +49,39 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client contact node
-        $clientContact = (new \NumNum\UBL\Contact())
+        $clientContact = (new Contact())
             ->setName('Client name')
             ->setElectronicMail('email@client.com')
             ->setTelephone('0032 472 123 456')
             ->setTelefax('0032 9 1234 567');
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address)
             ->setContact($clientContact);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
-        $commodityClassification = (new \NumNum\UBL\CommodityClassification())
+        $commodityClassification = (new CommodityClassification())
             ->setItemClassificationCode('123456')
             ->setItemClassificationListId('urn:ean.ucc:eanucc:2:2')
             ->setItemClassificationListVersionId('16');
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description')
             ->setSellersItemIdentification('SELLERID')
@@ -67,23 +89,23 @@ public function testIfXMLIsValid()
 
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // InvoicePeriod
-        $invoicePeriod = (new \NumNum\UBL\InvoicePeriod())
-            ->setStartDate(new \DateTime());
+        $invoicePeriod = (new InvoicePeriod())
+            ->setStartDate(new DateTime());
 
         // Invoice Line(s)
         $invoiceLines = [];
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -91,7 +113,7 @@ public function testIfXMLIsValid()
             ->setTaxTotal($lineTaxTotal)
             ->setInvoicedQuantity(1);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -100,7 +122,7 @@ public function testIfXMLIsValid()
             ->setTaxTotal($lineTaxTotal)
             ->setInvoicedQuantity(1);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -111,48 +133,48 @@ public function testIfXMLIsValid()
 
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
         $paymentMeans = [];
 
-        $payeeFinancialAccount = (new \NumNum\UBL\PayeeFinancialAccount())->setId('RO123456789012345');
-        $paymentMeans[] = (new \NumNum\UBL\PaymentMeans())
+        $payeeFinancialAccount = (new PayeeFinancialAccount())->setId('RO123456789012345');
+        $paymentMeans[] = (new PaymentMeans())
             ->setPaymentMeansCode(31)
-            ->setPaymentDueDate(new \DateTime())
+            ->setPaymentDueDate(new DateTime())
             ->setPayeeFinancialAccount($payeeFinancialAccount);
 
-        $payeeFinancialAccount = (new \NumNum\UBL\PayeeFinancialAccount())->setId('RO544456789067890');
-        $paymentMeans[] = (new \NumNum\UBL\PaymentMeans())
+        $payeeFinancialAccount = (new PayeeFinancialAccount())->setId('RO544456789067890');
+        $paymentMeans[] = (new PaymentMeans())
             ->setPaymentMeansCode(31)
-            ->setPaymentDueDate(new \DateTime())
+            ->setPaymentDueDate(new DateTime())
             ->setPayeeFinancialAccount($payeeFinancialAccount);
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setSupplierAssignedAccountId('10001')
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setPaymentMeans($paymentMeans)
@@ -162,12 +184,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/MultiplePaymentMeansTest.xml');
diff --git a/tests/Write/PartyIdentificationSchemeNameTest.php b/tests/Write/PartyIdentificationSchemeNameTest.php
index 54ab7b1..752ae99 100644
--- a/tests/Write/PartyIdentificationSchemeNameTest.php
+++ b/tests/Write/PartyIdentificationSchemeNameTest.php
@@ -2,6 +2,26 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\ContractDocumentReference;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoicePeriod;
+use NumNum\UBL\InvoiceTypeCode;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +29,17 @@
  */
 class PartyIdentificationSchemeNameTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,42 +47,42 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address)
             ->setPartyIdentificationSchemeName("SomeScheme");
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // Invoice Line(s)
-        $invoiceLine = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLine = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setPrice($price)
@@ -72,42 +92,42 @@ public function testIfXMLIsValid()
         $invoiceLines = [$invoiceLine];
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
-        $contractDocumentReference = (new \NumNum\UBL\ContractDocumentReference())
+        $contractDocumentReference = (new ContractDocumentReference())
             ->setId("123Test");
 
-        $invoicePeriod = (new \NumNum\UBL\InvoicePeriod())
-            ->setStartDate(new \DateTime('-31 days'))
-            ->setEndDate(new \DateTime());
+        $invoicePeriod = (new InvoicePeriod())
+            ->setStartDate(new DateTime('-31 days'))
+            ->setEndDate(new DateTime());
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setUBLVersionId('2.2')
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
-            ->setInvoiceTypeCode(\NumNum\UBL\InvoiceTypeCode::INVOICE)
-            ->setDueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
+            ->setInvoiceTypeCode(InvoiceTypeCode::INVOICE)
+            ->setDueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -119,12 +139,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/PartyIdentificationSchemeNameTest.xml');
diff --git a/tests/Write/ProjectReferenceTest.php b/tests/Write/ProjectReferenceTest.php
index b2daa54..313d281 100644
--- a/tests/Write/ProjectReferenceTest.php
+++ b/tests/Write/ProjectReferenceTest.php
@@ -2,7 +2,35 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\ClassifiedTaxCategory;
+use NumNum\UBL\Country;
+use NumNum\UBL\Delivery;
+use NumNum\UBL\FinancialInstitutionBranch;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoicePeriod;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalEntity;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\OrderReference;
+use NumNum\UBL\Party;
+use NumNum\UBL\PartyTaxScheme;
+use NumNum\UBL\PayeeFinancialAccount;
+use NumNum\UBL\PaymentMeans;
+use NumNum\UBL\PaymentTerms;
+use NumNum\UBL\Price;
+use NumNum\UBL\ProjectReference;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
 use NumNum\UBL\UNCL4461;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -10,51 +38,50 @@
  */
 class ProjectReferenceTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
-    private $xslfile = 'vendor/num-num/ubl-invoice/tests/EN16931-UBL-validation.xslt';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId('VAT');
 
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt 1')
             ->setAdditionalStreetName('Building A')
             ->setCityName('Gent')
             ->setPostalZone('9000')
             ->setCountry($country);
 
-        $financialInstitutionBranch = (new \NumNum\UBL\FinancialInstitutionBranch())
+        $financialInstitutionBranch = (new FinancialInstitutionBranch())
             ->setId('RABONL2U');
 
-        $payeeFinancialAccount = (new \NumNum\UBL\PayeeFinancialAccount())
+        $payeeFinancialAccount = (new PayeeFinancialAccount())
            ->setFinancialInstitutionBranch($financialInstitutionBranch)
             ->setName('Customer Account Holder')
             ->setId('NL00RABO0000000000');
 
-        $paymentMeans = (new \NumNum\UBL\PaymentMeans())
+        $paymentMeans = (new PaymentMeans())
             ->setPayeeFinancialAccount($payeeFinancialAccount)
             ->setPaymentMeansCode(UNCL4461::DEBIT_TRANSFER, [])
             ->setPaymentId('our invoice 1234');
 
         // Supplier company node
-        $supplierLegalEntity = (new \NumNum\UBL\LegalEntity())
+        $supplierLegalEntity = (new LegalEntity())
             ->setRegistrationName('Supplier Company Name')
             ->setCompanyId('BE123456789');
 
-        $supplierPartyTaxScheme = (new \NumNum\UBL\PartyTaxScheme())
+        $supplierPartyTaxScheme = (new PartyTaxScheme())
             ->setTaxScheme($taxScheme)
             ->setCompanyId('BE123456789');
 
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setLegalEntity($supplierLegalEntity)
             ->setPartyTaxScheme($supplierPartyTaxScheme)
@@ -62,55 +89,55 @@ public function testIfXMLIsValid()
             ->setPostalAddress($address);
 
         // Client company node
-        $clientLegalEntity = (new \NumNum\UBL\LegalEntity())
+        $clientLegalEntity = (new LegalEntity())
             ->setRegistrationName('Client Company Name')
             ->setCompanyId('Client Company Registration');
 
-        $clientPartyTaxScheme = (new \NumNum\UBL\PartyTaxScheme())
+        $clientPartyTaxScheme = (new PartyTaxScheme())
             ->setTaxScheme($taxScheme)
             ->setCompanyId('BE123456789');
 
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('Client Company Name')
             ->setLegalEntity($clientLegalEntity)
             ->setPartyTaxScheme($clientPartyTaxScheme)
             ->setPartyIdentificationId('BE123456789')
             ->setPostalAddress($address);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2.1)
             ->setAllowanceTotalAmount(0)
             ->setTaxInclusiveAmount(10 + 2.1)
             ->setLineExtensionAmount(10)
             ->setTaxExclusiveAmount(10);
 
-        $classifiedTaxCategory = (new \NumNum\UBL\ClassifiedTaxCategory())
+        $classifiedTaxCategory = (new ClassifiedTaxCategory())
             ->setId('S')
             ->setPercent(21.00)
             ->setTaxScheme($taxScheme);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setClassifiedTaxCategory($classifiedTaxCategory)
             ->setDescription('Product Description');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // InvoicePeriod
-        $invoicePeriod = (new \NumNum\UBL\InvoicePeriod())
-            ->setStartDate(new \DateTime());
+        $invoicePeriod = (new InvoicePeriod())
+            ->setStartDate(new DateTime());
 
         // Invoice Line(s)
-        $invoiceLine = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLine = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setPrice($price)
@@ -121,52 +148,52 @@ public function testIfXMLIsValid()
         $invoiceLines = [$invoiceLine];
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId('S', [])
             ->setPercent(21.00)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
         // Payment Terms
-        $paymentTerms = (new \NumNum\UBL\PaymentTerms())
+        $paymentTerms = (new PaymentTerms())
             ->setNote('30 days net');
 
         // Delivery
-        $deliveryLocation = (new \NumNum\UBL\Address())
+        $deliveryLocation = (new Address())
             ->setCountry($country);
 
-        $delivery = (new \NumNum\UBL\Delivery())
-            ->setActualDeliveryDate(new \DateTime())
+        $delivery = (new Delivery())
+            ->setActualDeliveryDate(new DateTime())
             ->setDeliveryLocation($deliveryLocation);
 
-        $orderReference = (new \NumNum\UBL\OrderReference())
+        $orderReference = (new OrderReference())
             ->setId('5009567')
             ->setSalesOrderId('tRST-tKhM');
 
         // Test Project Reference
-        $projectReference = (new \NumNum\UBL\ProjectReference())
+        $projectReference = (new ProjectReference())
             ->setId('Project1234');
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setCustomizationID('urn:cen.eu:en16931:2017')
             ->setId(1234)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setNote('invoice note')
             ->setDelivery($delivery)
             ->setAccountingSupplierParty($accountingSupplierParty)
@@ -183,12 +210,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument;
+        // used to validate the generated XML
+        $dom = new DOMDocument;
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/ProjectReferenceTest.xml');
diff --git a/tests/Write/SimpleCreditNoteTest.php b/tests/Write/SimpleCreditNoteTest.php
index 8dc1d38..3768478 100644
--- a/tests/Write/SimpleCreditNoteTest.php
+++ b/tests/Write/SimpleCreditNoteTest.php
@@ -2,6 +2,24 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\Country;
+use NumNum\UBL\CreditNote;
+use NumNum\UBL\CreditNoteLine;
+use NumNum\UBL\Generator;
+use NumNum\UBL\InvoiceTypeCode;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +27,17 @@
  */
 class SimpleCreditNoteTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-CreditNote-2.1.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-CreditNote-2.1.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,43 +45,43 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description')
             ->setSellersItemIdentification('SELLERID')
             ->setBuyersItemIdentification('BUYERID');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // Invoice Line(s)
-        $creditNoteLine = (new \NumNum\UBL\CreditNoteLine())
+        $creditNoteLine = (new CreditNoteLine())
             ->setId(0)
             ->setItem($productItem)
             ->setPrice($price)
@@ -73,47 +91,47 @@ public function testIfXMLIsValid()
         $creditNoteLines = [$creditNoteLine];
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setParty($clientCompany);
 
         // Invoice object
-        $creditNote = (new \NumNum\UBL\CreditNote())
+        $creditNote = (new CreditNote())
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setCreditNoteLines($creditNoteLines)
             ->setLegalMonetaryTotal($legalMonetaryTotal)
             ->setTaxTotal($taxTotal)
-            ->setInvoiceTypeCode(\NumNum\UBL\InvoiceTypeCode::CREDIT_NOTE);
+            ->setInvoiceTypeCode(InvoiceTypeCode::CREDIT_NOTE);
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->creditNote($creditNote);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/SimpleCreditNoteTest.xml');
diff --git a/tests/Write/SimpleDebitNoteTest.php b/tests/Write/SimpleDebitNoteTest.php
index 40c10bf..42d3efd 100644
--- a/tests/Write/SimpleDebitNoteTest.php
+++ b/tests/Write/SimpleDebitNoteTest.php
@@ -2,6 +2,23 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\Country;
+use NumNum\UBL\DebitNote;
+use NumNum\UBL\DebitNoteLine;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +26,17 @@
  */
 class SimpleDebitNoteTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-DebitNote-2.1.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-DebitNote-2.1.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,43 +44,43 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description')
             ->setSellersItemIdentification('SELLERID')
             ->setBuyersItemIdentification('BUYERID');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // Debit Note Line(s)
-        $debitNoteLine = (new \NumNum\UBL\DebitNoteLine())
+        $debitNoteLine = (new DebitNoteLine())
             ->setId(0)
             ->setItem($productItem)
             ->setPrice($price)
@@ -73,32 +90,32 @@ public function testIfXMLIsValid()
         $debitNoteLines = [$debitNoteLine];
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setParty($clientCompany);
 
         // Debit Note object
-        $debitNote = (new \NumNum\UBL\DebitNote())
+        $debitNote = (new DebitNote())
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setDebitNoteLines($debitNoteLines)
@@ -107,12 +124,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->debitNote($debitNote);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/SimpleDebitNoteTest.xml');
diff --git a/tests/Write/SimpleInvoiceTest.php b/tests/Write/SimpleInvoiceTest.php
index 5208312..1dfe0f2 100644
--- a/tests/Write/SimpleInvoiceTest.php
+++ b/tests/Write/SimpleInvoiceTest.php
@@ -2,6 +2,26 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\Contact;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoicePeriod;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\OrderLineReference;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +29,17 @@
  */
 class SimpleInvoiceTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,59 +47,59 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client contact node
-        $clientContact = (new \NumNum\UBL\Contact())
+        $clientContact = (new Contact())
             ->setName('Client name')
             ->setElectronicMail('email@client.com')
             ->setTelephone('0032 472 123 456')
             ->setTelefax('0032 9 1234 567');
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address)
             ->setContact($clientContact);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description')
             ->setSellersItemIdentification('SELLERID');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // InvoicePeriod
-        $invoicePeriod = (new \NumNum\UBL\InvoicePeriod())
-            ->setStartDate(new \DateTime());
+        $invoicePeriod = (new InvoicePeriod())
+            ->setStartDate(new DateTime());
 
         // Invoice Line(s)
         $invoiceLines = [];
 
-        $orderLineReference = (new \NumNum\UBL\OrderLineReference())
+        $orderLineReference = (new OrderLineReference())
             ->setLineId('#ABC123');
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -88,7 +108,7 @@ public function testIfXMLIsValid()
             ->setInvoicedQuantity(1)
             ->setOrderLineReference($orderLineReference);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -98,7 +118,7 @@ public function testIfXMLIsValid()
             ->setInvoicedQuantity(1)
             ->setOrderLineReference($orderLineReference);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -110,35 +130,35 @@ public function testIfXMLIsValid()
 
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setSupplierAssignedAccountId('10001')
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
-            ->setIssueTime(new \DateTime())
+            ->setIssueDate(new DateTime())
+            ->setIssueTime(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -147,12 +167,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/SimpleInvoiceTest.xml');
diff --git a/tests/Write/SimpleInvoiceWithExternalReferenceTest.php b/tests/Write/SimpleInvoiceWithExternalReferenceTest.php
index 093b4cd..a5e1a5e 100644
--- a/tests/Write/SimpleInvoiceWithExternalReferenceTest.php
+++ b/tests/Write/SimpleInvoiceWithExternalReferenceTest.php
@@ -2,6 +2,28 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\AdditionalDocumentReference;
+use NumNum\UBL\Address;
+use NumNum\UBL\Attachment;
+use NumNum\UBL\Contact;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoicePeriod;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\OrderLineReference;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +31,17 @@
  */
 class SimpleInvoiceWithExternalReferenceTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,59 +49,59 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client contact node
-        $clientContact = (new \NumNum\UBL\Contact())
+        $clientContact = (new Contact())
             ->setName('Client name')
             ->setElectronicMail('email@client.com')
             ->setTelephone('0032 472 123 456')
             ->setTelefax('0032 9 1234 567');
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address)
             ->setContact($clientContact);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description')
             ->setSellersItemIdentification('SELLERID');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // InvoicePeriod
-        $invoicePeriod = (new \NumNum\UBL\InvoicePeriod())
-            ->setStartDate(new \DateTime());
+        $invoicePeriod = (new InvoicePeriod())
+            ->setStartDate(new DateTime());
 
         // Invoice Line(s)
         $invoiceLines = [];
 
-        $orderLineReference = (new \NumNum\UBL\OrderLineReference())
+        $orderLineReference = (new OrderLineReference())
             ->setLineId('#ABC123');
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -88,7 +110,7 @@ public function testIfXMLIsValid()
             ->setInvoicedQuantity(1)
             ->setOrderLineReference($orderLineReference);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -98,7 +120,7 @@ public function testIfXMLIsValid()
             ->setInvoicedQuantity(1)
             ->setOrderLineReference($orderLineReference);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -110,43 +132,43 @@ public function testIfXMLIsValid()
 
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
-        $attachment = (new \NumNum\UBL\Attachment())
+        $attachment = (new Attachment())
             ->setExternalReference('http://www.suppliersite.eu/sheet001.html');
 
-        $additionalDocumentReference = (new \NumNum\UBL\AdditionalDocumentReference())
+        $additionalDocumentReference = (new AdditionalDocumentReference())
             ->setId('Doc1')
             ->setDocumentType('Timesheet')
             ->setAttachment($attachment);
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setSupplierAssignedAccountId('10001')
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setId(1234)
             ->setAdditionalDocumentReference($additionalDocumentReference)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -155,12 +177,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/SimpleInvoiceWithExternalReferenceTest.xml');
diff --git a/tests/Write/SimpleInvoiceWithFilePathPdfTest.php b/tests/Write/SimpleInvoiceWithFilePathPdfTest.php
index 56b6efb..0346edb 100644
--- a/tests/Write/SimpleInvoiceWithFilePathPdfTest.php
+++ b/tests/Write/SimpleInvoiceWithFilePathPdfTest.php
@@ -2,6 +2,28 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\AdditionalDocumentReference;
+use NumNum\UBL\Address;
+use NumNum\UBL\Attachment;
+use NumNum\UBL\Contact;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoicePeriod;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\OrderLineReference;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +31,17 @@
  */
 class SimpleInvoiceWithFilePathPdfTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,59 +49,59 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client contact node
-        $clientContact = (new \NumNum\UBL\Contact())
+        $clientContact = (new Contact())
             ->setName('Client name')
             ->setElectronicMail('email@client.com')
             ->setTelephone('0032 472 123 456')
             ->setTelefax('0032 9 1234 567');
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address)
             ->setContact($clientContact);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description')
             ->setSellersItemIdentification('SELLERID');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // InvoicePeriod
-        $invoicePeriod = (new \NumNum\UBL\InvoicePeriod())
-            ->setStartDate(new \DateTime());
+        $invoicePeriod = (new InvoicePeriod())
+            ->setStartDate(new DateTime());
 
         // Invoice Line(s)
         $invoiceLines = [];
 
-        $orderLineReference = (new \NumNum\UBL\OrderLineReference())
+        $orderLineReference = (new OrderLineReference())
             ->setLineId('#ABC123');
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -88,7 +110,7 @@ public function testIfXMLIsValid()
             ->setInvoicedQuantity(1)
             ->setOrderLineReference($orderLineReference);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -98,7 +120,7 @@ public function testIfXMLIsValid()
             ->setInvoicedQuantity(1)
             ->setOrderLineReference($orderLineReference);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -110,41 +132,48 @@ public function testIfXMLIsValid()
 
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
-        $attachment = (new \NumNum\UBL\Attachment())
-            ->setFilePath(__DIR__.DIRECTORY_SEPARATOR.'..'.DIRECTORY_SEPARATOR.'Files'.DIRECTORY_SEPARATOR.'SampleInvoice.pdf');
-
-        $additionalDocumentReference = (new \NumNum\UBL\AdditionalDocumentReference())
+        $attachmentFilePath = __DIR__
+            .DIRECTORY_SEPARATOR
+            .'..'
+            .DIRECTORY_SEPARATOR
+            .'Files'
+            .DIRECTORY_SEPARATOR
+            .'SampleInvoice.pdf';
+        $attachment = (new Attachment())
+            ->setFilePath($attachmentFilePath);
+
+        $additionalDocumentReference = (new AdditionalDocumentReference())
             ->setAttachment($attachment);
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setSupplierAssignedAccountId('10001')
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setId(1234)
             ->setAdditionalDocumentReference($additionalDocumentReference)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -153,12 +182,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/SimpleInvoiceWithFilePathPdfTest.xml');
diff --git a/tests/Write/SimpleInvoiceWithInlinePdfTest.php b/tests/Write/SimpleInvoiceWithInlinePdfTest.php
index ca3e18c..9da7988 100644
--- a/tests/Write/SimpleInvoiceWithInlinePdfTest.php
+++ b/tests/Write/SimpleInvoiceWithInlinePdfTest.php
@@ -2,6 +2,28 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\AdditionalDocumentReference;
+use NumNum\UBL\Address;
+use NumNum\UBL\Attachment;
+use NumNum\UBL\Contact;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\InvoicePeriod;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\OrderLineReference;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,17 +31,17 @@
  */
 class SimpleInvoiceWithInlinePdfTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -27,59 +49,59 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client contact node
-        $clientContact = (new \NumNum\UBL\Contact())
+        $clientContact = (new Contact())
             ->setName('Client name')
             ->setElectronicMail('email@client.com')
             ->setTelephone('0032 472 123 456')
             ->setTelefax('0032 9 1234 567');
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address)
             ->setContact($clientContact);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description')
             ->setSellersItemIdentification('SELLERID');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // InvoicePeriod
-        $invoicePeriod = (new \NumNum\UBL\InvoicePeriod())
-            ->setStartDate(new \DateTime());
+        $invoicePeriod = (new InvoicePeriod())
+            ->setStartDate(new DateTime());
 
         // Invoice Line(s)
         $invoiceLines = [];
 
-        $orderLineReference = (new \NumNum\UBL\OrderLineReference())
+        $orderLineReference = (new OrderLineReference())
             ->setLineId('#ABC123');
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -88,7 +110,7 @@ public function testIfXMLIsValid()
             ->setInvoicedQuantity(1)
             ->setOrderLineReference($orderLineReference);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -98,7 +120,7 @@ public function testIfXMLIsValid()
             ->setInvoicedQuantity(1)
             ->setOrderLineReference($orderLineReference);
 
-        $invoiceLines[] = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLines[] = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setInvoicePeriod($invoicePeriod)
@@ -110,46 +132,53 @@ public function testIfXMLIsValid()
 
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
         // Example if you have some inline or in-memory filestream/file contents
-        $fileStream = file_get_contents(__DIR__.DIRECTORY_SEPARATOR.'..'.DIRECTORY_SEPARATOR.'Files'.DIRECTORY_SEPARATOR.'SampleInvoice.pdf'); // this would be your file contents
+        $fileStreamFileName = __DIR__
+            .DIRECTORY_SEPARATOR
+            .'..'
+            .DIRECTORY_SEPARATOR
+            .'Files'
+            .DIRECTORY_SEPARATOR
+            .'SampleInvoice.pdf';
+        $fileStream = file_get_contents($fileStreamFileName); // this would be your file contents
 
         $base64EncodedFileStream = base64_encode($fileStream);
 
-        $attachment = (new \NumNum\UBL\Attachment())
+        $attachment = (new Attachment())
             ->setBase64Content($base64EncodedFileStream, 'Invoice.pdf', 'application/pdf');
 
-        $additionalDocumentReference = (new \NumNum\UBL\AdditionalDocumentReference())
+        $additionalDocumentReference = (new AdditionalDocumentReference())
             ->setAttachment($attachment);
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setSupplierAssignedAccountId('10001')
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setId(1234)
             ->setAdditionalDocumentReference($additionalDocumentReference)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -158,12 +187,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/SimpleInvoiceWithInlinePdfTest.xml');
diff --git a/tests/Write/SimpleUBL22InvoiceTest.php b/tests/Write/SimpleUBL22InvoiceTest.php
index 1c95e57..8c63ab4 100644
--- a/tests/Write/SimpleUBL22InvoiceTest.php
+++ b/tests/Write/SimpleUBL22InvoiceTest.php
@@ -2,6 +2,23 @@
 
 namespace NumNum\UBL\Tests\Write;
 
+use DateTime;
+use DOMDocument;
+use NumNum\UBL\AccountingParty;
+use NumNum\UBL\Address;
+use NumNum\UBL\Country;
+use NumNum\UBL\Generator;
+use NumNum\UBL\Invoice;
+use NumNum\UBL\InvoiceLine;
+use NumNum\UBL\Item;
+use NumNum\UBL\LegalMonetaryTotal;
+use NumNum\UBL\Party;
+use NumNum\UBL\Price;
+use NumNum\UBL\TaxCategory;
+use NumNum\UBL\TaxScheme;
+use NumNum\UBL\TaxSubTotal;
+use NumNum\UBL\TaxTotal;
+use NumNum\UBL\UnitCode;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -9,18 +26,18 @@
  */
 class SimpleUBL22InvoiceTest extends TestCase
 {
-    private $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
+    private string $schema = 'http://docs.oasis-open.org/ubl/os-UBL-2.2/xsd/maindoc/UBL-Invoice-2.2.xsd';
 
     /** @test */
     public function testIfXMLIsValid()
     {
         // Address country
-        $country = (new \NumNum\UBL\Country())
+        $country = (new Country())
             ->setIdentificationCode('BE')
             ->setListId('ISO3166-1:Alpha2');
 
         // Full address
-        $address = (new \NumNum\UBL\Address())
+        $address = (new Address())
             ->setStreetName('Korenmarkt')
             ->setBuildingNumber(1)
             ->setCityName('Gent')
@@ -28,42 +45,42 @@ public function testIfXMLIsValid()
             ->setCountry($country);
 
         // Supplier company node
-        $supplierCompany = (new \NumNum\UBL\Party())
+        $supplierCompany = (new Party())
             ->setName('Supplier Company Name')
             ->setPhysicalLocation($address)
             ->setPostalAddress($address);
 
         // Client company node
-        $clientCompany = (new \NumNum\UBL\Party())
+        $clientCompany = (new Party())
             ->setName('My client')
             ->setPostalAddress($address);
 
-        $legalMonetaryTotal = (new \NumNum\UBL\LegalMonetaryTotal())
+        $legalMonetaryTotal = (new LegalMonetaryTotal())
             ->setPayableAmount(10 + 2)
             ->setAllowanceTotalAmount(0);
 
         // Tax scheme
-        $taxScheme = (new \NumNum\UBL\TaxScheme())
+        $taxScheme = (new TaxScheme())
             ->setId(0);
 
         // Product
-        $productItem = (new \NumNum\UBL\Item())
+        $productItem = (new Item())
             ->setName('Product Name')
             ->setDescription('Product Description');
 
         // Price
-        $price = (new \NumNum\UBL\Price())
+        $price = (new Price())
             ->setBaseQuantity(1)
-            ->setUnitCode(\NumNum\UBL\UnitCode::UNIT)
+            ->setUnitCode(UnitCode::UNIT)
             ->setUnitCodeListId('UNECERec20')
             ->setPriceAmount(10);
 
         // Invoice Line tax totals
-        $lineTaxTotal = (new \NumNum\UBL\TaxTotal())
+        $lineTaxTotal = (new TaxTotal())
             ->setTaxAmount(2.1);
 
         // Invoice Line(s)
-        $invoiceLine = (new \NumNum\UBL\InvoiceLine())
+        $invoiceLine = (new InvoiceLine())
             ->setId(0)
             ->setItem($productItem)
             ->setUnitCode('C62')
@@ -75,33 +92,33 @@ public function testIfXMLIsValid()
         $invoiceLines = [$invoiceLine];
 
         // Total Taxes
-        $taxCategory = (new \NumNum\UBL\TaxCategory())
+        $taxCategory = (new TaxCategory())
             ->setId(0)
             ->setName('VAT21%')
             ->setPercent(.21)
             ->setTaxScheme($taxScheme);
 
-        $taxSubTotal = (new \NumNum\UBL\TaxSubTotal())
+        $taxSubTotal = (new TaxSubTotal())
             ->setTaxableAmount(10)
             ->setTaxAmount(2.1)
             ->setTaxCategory($taxCategory);
 
-        $taxTotal = (new \NumNum\UBL\TaxTotal())
+        $taxTotal = (new TaxTotal())
             ->addTaxSubTotal($taxSubTotal)
             ->setTaxAmount(2.1);
 
-        $accountingSupplierParty = (new \NumNum\UBL\AccountingParty())
+        $accountingSupplierParty = (new AccountingParty())
             ->setParty($supplierCompany);
 
-        $accountingCustomerParty = (new \NumNum\UBL\AccountingParty())
+        $accountingCustomerParty = (new AccountingParty())
             ->setParty($clientCompany);
 
         // Invoice object
-        $invoice = (new \NumNum\UBL\Invoice())
+        $invoice = (new Invoice())
             ->setUBLVersionId('2.2')
             ->setId(1234)
             ->setCopyIndicator(false)
-            ->setIssueDate(new \DateTime())
+            ->setIssueDate(new DateTime())
             ->setAccountingSupplierParty($accountingSupplierParty)
             ->setAccountingCustomerParty($accountingCustomerParty)
             ->setInvoiceLines($invoiceLines)
@@ -110,12 +127,12 @@ public function testIfXMLIsValid()
 
         // Test created object
         // Use \NumNum\UBL\Generator to generate an XML string
-        $generator = new \NumNum\UBL\Generator();
+        $generator = new Generator();
         $outputXMLString = $generator->invoice($invoice);
 
         // Create PHP Native DomDocument object, that can be
-        // used to validate the generate XML
-        $dom = new \DOMDocument();
+        // used to validate the generated XML
+        $dom = new DOMDocument();
         $dom->loadXML($outputXMLString);
 
         $dom->save('./tests/SimpleUBL22InvoiceTest.xml');