Merge pull request #1 from lou-perret/master

Fix deprecations on PHP 8.1

Author: bseddon

src/Asn1/Der/Encoder.php

@@ -296,13 +296,13 @@ protected function encodeType($typeID, $class, $isConstructed)
     /**
      * Encode the length of the encoded value of an element.
      *
-     * @param string $encodedElementValue the encoded value of an element
+     * @param ?string $encodedElementValue the encoded value of an element
      *
      * @return string
      */
     protected function encodeLength($encodedElementValue)
     {
-        $length = strlen($encodedElementValue);
+        $length = $encodedElementValue === null ? 0 : strlen($encodedElementValue);
         if ($length < 128) {
             return chr($length);
         }