diff --git a/build/Project.csproj.props b/build/Project.csproj.props
index 1d004b4..c1df222 100644
--- a/build/Project.csproj.props
+++ b/build/Project.csproj.props
@@ -1,5 +1,2 @@
 <Project>
-  <PropertyGroup>
-    <Nullable>annotations</Nullable>
-  </PropertyGroup>
 </Project>
\ No newline at end of file
diff --git a/src/Firmware.cs b/src/Firmware.cs
index d3e78b0..6992162 100644
--- a/src/Firmware.cs
+++ b/src/Firmware.cs
@@ -169,7 +169,7 @@ public class PortPinInfo
     /// Specifies the microcontroller port where the pin is located.
     /// </summary>
     [YamlMember(Order = -1)]
-    public string Port;
+    public string Port = "";
 
     /// <summary>
     /// Specifies the unique pin number in the defined port.
@@ -357,12 +357,9 @@ class PortPinInfoTypeConverter(IDeserializer deserializer) : IYamlTypeConverter
 
     public IDeserializer Deserializer { get; } = deserializer ?? throw new ArgumentNullException(nameof(deserializer));
 
-    public bool Accepts(Type type)
-    {
-        return type == typeof(PortPinInfo);
-    }
+    public bool Accepts(Type type) => type == typeof(PortPinInfo);
 
-    public object ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeserializer)
+    public object? ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeserializer)
     {
         var portPin = Deserializer.Deserialize<Dictionary<object, object>>(parser);
         if (portPin.TryGetValue(DirectionProperty, out object value))
@@ -381,7 +378,7 @@ public object ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeseria
         throw new YamlException($"Required property '{DirectionProperty}' not found when deserializing type '{typeof(PortPinInfo)}'.");
     }
 
-    public void WriteYaml(IEmitter emitter, object value, Type type, ObjectSerializer serializer)
+    public void WriteYaml(IEmitter emitter, object? value, Type type, ObjectSerializer serializer)
     {
         throw new NotImplementedException();
     }
@@ -397,6 +394,9 @@ class LowerCaseEnumTypeConverter : IYamlTypeConverter
 
     public void WriteYaml(IEmitter emitter, object? value, Type type, ObjectSerializer serializer)
     {
+        if (value is null)
+            return;
+
         var scalarStyle = ScalarStyle.Any;
         var scalarValue = LowerCaseNamingConvention.Instance.Apply(value.ToString());
         if (scalarValue == "off")
@@ -415,6 +415,9 @@ class CamelCaseEnumTypeConverter : IYamlTypeConverter
 
     public void WriteYaml(IEmitter emitter, object? value, Type type, ObjectSerializer serializer)
     {
+        if (value is null)
+            return;
+
         emitter.Emit(new Scalar(CamelCaseNamingConvention.Instance.Apply(value.ToString())));
     }
 }
diff --git a/src/Interface.cs b/src/Interface.cs
index b000b0c..c35e682 100644
--- a/src/Interface.cs
+++ b/src/Interface.cs
@@ -18,7 +18,7 @@ public class DeviceInfo
     /// <summary>
     /// Specifies the name of the device.
     /// </summary>
-    public string Device;
+    public string Device = "";
 
     /// <summary>
     /// Specifies the unique identifier for this device type.
@@ -28,12 +28,12 @@ public class DeviceInfo
     /// <summary>
     /// Specifies the version of the device firmware.
     /// </summary>
-    public HarpVersion FirmwareVersion;
+    public HarpVersion? FirmwareVersion;
 
     /// <summary>
     /// Specifies the version of the device hardware.
     /// </summary>
-    public HarpVersion HardwareTargets;
+    public HarpVersion? HardwareTargets;
 
     /// <summary>
     /// Specifies the collection of registers implementing the device function.
@@ -151,7 +151,7 @@ public class RegisterInfo
     /// <summary>
     /// Specifies the name of the bit mask or group mask used to represent the payload value.
     /// </summary>
-    public string MaskType;
+    public string MaskType = "";
 
     /// <summary>
     /// Specifies the minimum allowable value for the payload.
@@ -171,7 +171,7 @@ public class RegisterInfo
     /// <summary>
     /// Specifies the name of the type used to represent the payload value in the high-level interface.
     /// </summary>
-    public string InterfaceType;
+    public string InterfaceType = "";
 
     /// <summary>
     /// Specifies a custom converter which will be used to parse or format the payload value.
@@ -187,7 +187,7 @@ public class RegisterInfo
     /// Specifies a collection of payload members describing the contents
     /// of the raw payload value.
     /// </summary>
-    public Dictionary<string, PayloadMemberInfo> PayloadSpec;
+    public Dictionary<string, PayloadMemberInfo>? PayloadSpec;
 
     /// <summary>
     /// Gets a value indicating whether a custom converter will be used to parse or
@@ -229,7 +229,7 @@ public class PayloadMemberInfo
     /// <summary>
     /// Specifies the name of the bit mask or group mask used to represent this payload member.
     /// </summary>
-    public string MaskType;
+    public string MaskType = "";
 
     /// <summary>
     /// Specifies the minimum allowable value for this payload member.
@@ -249,7 +249,7 @@ public class PayloadMemberInfo
     /// <summary>
     /// Specifies the name of the type used to represent this payload member in the high-level interface.
     /// </summary>
-    public string InterfaceType;
+    public string InterfaceType = "";
 
     /// <summary>
     /// Specifies a custom converter which will be used to parse or format this payload member.
@@ -350,7 +350,7 @@ public class MaskValue
     /// <summary>
     /// Specifies a summary description of the mask value function.
     /// </summary>
-    public string Description;
+    public string Description = "";
 }
 
 internal static partial class TemplateHelper
@@ -478,7 +478,9 @@ public static string GetParseConversion(RegisterInfo register, string expression
         else if (register.InterfaceType == "string")
             return $"PayloadMarshal.ReadUtf8String({expression})";
         else
-            return GetConversionToInterfaceType(register.InterfaceType ?? register.MaskType, expression);
+            return GetConversionToInterfaceType(
+                string.IsNullOrEmpty(register.InterfaceType) ? register.MaskType : register.InterfaceType,
+                expression);
     }
 
     public static string GetFormatConversion(RegisterInfo register, string expression)
@@ -486,7 +488,10 @@ public static string GetFormatConversion(RegisterInfo register, string expressio
         if (register.PayloadSpec != null || register.InterfaceType == "string" || register.HasConverter)
             return $"FormatPayload({expression})";
         else
-            return GetConversionFromInterfaceType(register.InterfaceType ?? register.MaskType, register.PayloadInterfaceType, expression);
+            return GetConversionFromInterfaceType(
+                string.IsNullOrEmpty(register.InterfaceType) ? register.MaskType : register.InterfaceType,
+                register.PayloadInterfaceType,
+                expression);
     }
 
     public static string GetConversionToInterfaceType(string interfaceType, string expression)
@@ -608,7 +613,9 @@ public static string GetPayloadMemberParser(
         {
             return $"ParsePayload{name}({expression})";
         }
-        return GetConversionToInterfaceType(member.InterfaceType ?? member.MaskType, expression);
+        return GetConversionToInterfaceType(
+            string.IsNullOrEmpty(member.InterfaceType) ? member.MaskType : member.InterfaceType,
+            expression);
     }
 
     public static string GetPayloadMemberAssignmentFormatter(
@@ -661,7 +668,8 @@ public static string GetPayloadMemberValueFormatter(
 
         var isBoolean = member.InterfaceType == "bool" && !member.HasConverter;
         var payloadInterfaceType = GetInterfaceType(payloadType);
-        if (!string.IsNullOrEmpty(member.InterfaceType ?? member.MaskType))
+        var memberInterfaceType = string.IsNullOrEmpty(member.InterfaceType) ? member.MaskType : member.InterfaceType;
+        if (!string.IsNullOrEmpty(memberInterfaceType))
         {
             if (isBoolean)
             {
@@ -697,10 +705,7 @@ class HarpVersionTypeConverter : IYamlTypeConverter
 {
     public static readonly HarpVersionTypeConverter Instance = new();
 
-    public bool Accepts(Type type)
-    {
-        return type == typeof(HarpVersion);
-    }
+    public bool Accepts(Type type) => type == typeof(HarpVersion);
 
     public object ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeserializer)
     {
@@ -708,12 +713,15 @@ public object ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeseria
         return HarpVersion.Parse(scalar.Value);
     }
 
-    public void WriteYaml(IEmitter emitter, object value, Type type, ObjectSerializer serializer)
+    public void WriteYaml(IEmitter emitter, object? value, Type type, ObjectSerializer serializer)
     {
+        if (value is not HarpVersion version)
+            return;
+
         var scalar = new Scalar(
             AnchorName.Empty,
             TagName.Empty,
-            ((HarpVersion)value).ToString(),
+            version.ToString(),
             ScalarStyle.DoubleQuoted,
             isPlainImplicit: false,
             isQuotedImplicit: true);
@@ -727,12 +735,12 @@ class HexValueTypeConverter : IYamlTypeConverter
 
     public bool Accepts(Type type) => false;
 
-    public object ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeserializer)
+    public object? ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeserializer)
     {
         return rootDeserializer(type);
     }
 
-    public void WriteYaml(IEmitter emitter, object value, Type type, ObjectSerializer serializer)
+    public void WriteYaml(IEmitter emitter, object? value, Type type, ObjectSerializer serializer)
     {
         emitter.Emit(new Scalar(string.Format($"0x{value:X}")));
     }
@@ -750,17 +758,14 @@ class MaskValueTypeConverter : IYamlTypeConverter
         .WithTypeConverter(HexValueTypeConverter.Instance)
         .BuildValueSerializer();
 
-    public bool Accepts(Type type)
-    {
-        return type == typeof(MaskValue);
-    }
+    public bool Accepts(Type type) => type == typeof(MaskValue);
 
-    public object ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeserializer)
+    public object? ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeserializer)
     {
-        if (parser.TryConsume(out MappingStart _))
+        if (parser.TryConsume<MappingStart>(out var _))
         {
             var maskValue = new MaskValue();
-            while (!parser.TryConsume(out MappingEnd _))
+            while (!parser.TryConsume<MappingEnd>(out var _))
             {
                 var key = parser.Consume<Scalar>();
                 var value = parser.Consume<Scalar>();
@@ -786,9 +791,11 @@ public object ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeseria
         }
     }
 
-    public void WriteYaml(IEmitter emitter, object value, Type type, ObjectSerializer serializer)
+    public void WriteYaml(IEmitter emitter, object? value, Type type, ObjectSerializer serializer)
     {
-        var maskValue = (MaskValue)value;
+        if (value is not MaskValue maskValue)
+            return;
+
         if (string.IsNullOrEmpty(maskValue.Description))
             HexValueTypeConverter.Instance.WriteYaml(emitter, maskValue.Value, typeof(int), serializer);
         else
@@ -800,17 +807,14 @@ class RegisterAccessTypeConverter : IYamlTypeConverter
 {
     public static readonly RegisterAccessTypeConverter Instance = new();
 
-    public bool Accepts(Type type)
-    {
-        return type == typeof(RegisterAccess);
-    }
+    public bool Accepts(Type type) => type == typeof(RegisterAccess);
 
-    public object ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeserializer)
+    public object? ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeserializer)
     {
-        if (parser.TryConsume(out SequenceStart _))
+        if (parser.TryConsume<SequenceStart>(out var _))
         {
             RegisterAccess value = 0;
-            while (parser.TryConsume(out Scalar scalar))
+            while (parser.TryConsume<Scalar>(out var scalar))
             {
                 value |= (RegisterAccess)Enum.Parse(typeof(RegisterAccess), scalar.Value);
             }
@@ -824,9 +828,11 @@ public object ReadYaml(IParser parser, Type type, ObjectDeserializer rootDeseria
         }
     }
 
-    public void WriteYaml(IEmitter emitter, object value, Type type, ObjectSerializer serializer)
+    public void WriteYaml(IEmitter emitter, object? value, Type type, ObjectSerializer serializer)
     {
-        var access = (RegisterAccess)value;
+        if (value is not RegisterAccess access)
+            return;
+
         switch (access)
         {
             case RegisterAccess.Read:
diff --git a/src/TemplateBase.cs b/src/TemplateBase.cs
index 61f4fdd..aae5471 100644
--- a/src/TemplateBase.cs
+++ b/src/TemplateBase.cs
@@ -7,12 +7,12 @@ namespace Harp.Generators;
 
 internal abstract class TemplateBase
 {
-    private StringBuilder builder;
-    private CompilerErrorCollection errors;
+    private StringBuilder? builder;
+    private CompilerErrorCollection? errors;
     private string currentIndent = string.Empty;
-    private Stack<int> indents;
+    private Stack<int>? indents;
 
-    public virtual IDictionary<string, object> Session { get; set; }
+    public virtual IDictionary<string, object>? Session { get; set; }
 
     public string FileName { get; set; } = string.Empty;
 
diff --git a/tests/FirmwareGeneratorTests.cs b/tests/FirmwareGeneratorTests.cs
index 7de67c3..a7d364c 100644
--- a/tests/FirmwareGeneratorTests.cs
+++ b/tests/FirmwareGeneratorTests.cs
@@ -5,7 +5,7 @@ namespace Harp.Generators.Tests;
 [TestClass]
 public sealed class FirmwareGeneratorTests
 {
-    DirectoryInfo outputDirectory;
+    DirectoryInfo? outputDirectory;
 
     [TestInitialize]
     public void Initialize()
@@ -49,14 +49,17 @@ public void FirmwareTemplate_GenerateAndBuild(string metadataFileName, params st
         }
         catch (AssertFailedException)
         {
-            outputDirectory.Create();
-            File.WriteAllText(Path.Combine(outputDirectory.FullName, appOutputFileName), headers.App);
-            File.WriteAllText(Path.Combine(outputDirectory.FullName, appImplOutputFileName), implementation.App);
-            File.WriteAllText(Path.Combine(outputDirectory.FullName, appFuncsOutputFileName), headers.AppFuncs);
-            File.WriteAllText(Path.Combine(outputDirectory.FullName, appFuncsImplOutputFileName), implementation.AppFuncs);
-            File.WriteAllText(Path.Combine(outputDirectory.FullName, appRegsOutputFileName), headers.AppRegs);
-            File.WriteAllText(Path.Combine(outputDirectory.FullName, appRegsImplOutputFileName), implementation.AppRegs);
-            File.WriteAllText(Path.Combine(outputDirectory.FullName, interruptsOutputFileName), implementation.Interrupts);
+            if (outputDirectory is not null)
+            {
+                outputDirectory.Create();
+                File.WriteAllText(Path.Combine(outputDirectory.FullName, appOutputFileName), headers.App);
+                File.WriteAllText(Path.Combine(outputDirectory.FullName, appImplOutputFileName), implementation.App);
+                File.WriteAllText(Path.Combine(outputDirectory.FullName, appFuncsOutputFileName), headers.AppFuncs);
+                File.WriteAllText(Path.Combine(outputDirectory.FullName, appFuncsImplOutputFileName), implementation.AppFuncs);
+                File.WriteAllText(Path.Combine(outputDirectory.FullName, appRegsOutputFileName), headers.AppRegs);
+                File.WriteAllText(Path.Combine(outputDirectory.FullName, appRegsImplOutputFileName), implementation.AppRegs);
+                File.WriteAllText(Path.Combine(outputDirectory.FullName, interruptsOutputFileName), implementation.Interrupts);
+            }
             throw;
         }
     }
diff --git a/tests/InterfaceGeneratorTests.cs b/tests/InterfaceGeneratorTests.cs
index a9eda41..4998b8c 100644
--- a/tests/InterfaceGeneratorTests.cs
+++ b/tests/InterfaceGeneratorTests.cs
@@ -5,8 +5,8 @@ namespace Harp.Generators.Tests;
 [TestClass]
 public sealed class InterfaceGeneratorTests
 {
-    DirectoryInfo outputDirectory;
-    string payloadExtensions;
+    DirectoryInfo? outputDirectory;
+    string payloadExtensions = "";
 
     [TestInitialize]
     public void Initialize()
@@ -24,7 +24,7 @@ public void DeviceTemplate_GenerateAndBuildWithoutErrors(string metadataFileName
     {
         metadataFileName = TestHelper.GetMetadataPath(metadataFileName);
         var deviceMetadata = TestHelper.ReadDeviceMetadata(metadataFileName);
-        var generator = new InterfaceGenerator(deviceMetadata, typeof(InterfaceGeneratorTests).Namespace);
+        var generator = new InterfaceGenerator(deviceMetadata, typeof(InterfaceGeneratorTests).Namespace ?? "");
         var implementation = generator.GenerateImplementation();
         var outputFileName = Path.GetFileNameWithoutExtension(metadataFileName);
         var deviceOutputFileName = $"{outputFileName}.cs";
@@ -32,16 +32,18 @@ public void DeviceTemplate_GenerateAndBuildWithoutErrors(string metadataFileName
         var customImplementation = TestHelper.GetManifestResourceText($"EmbeddedSources.{outputFileName}.cs");
         try
         {
-            TestHelper.AssertNoGeneratorErrors(generator.Errors);
             CompilerTestHelper.CompileFromSource(implementation.Device, implementation.AsyncDevice, payloadExtensions, customImplementation);
             TestHelper.AssertExpectedOutput(implementation.Device, deviceOutputFileName);
             TestHelper.AssertExpectedOutput(implementation.AsyncDevice, asyncDeviceOutputFileName);
         }
         catch (AssertFailedException)
         {
-            outputDirectory.Create();
-            File.WriteAllText(Path.Combine(outputDirectory.FullName, deviceOutputFileName), implementation.Device);
-            File.WriteAllText(Path.Combine(outputDirectory.FullName, asyncDeviceOutputFileName), implementation.AsyncDevice);
+            if (outputDirectory is not null)
+            {
+                outputDirectory.Create();
+                File.WriteAllText(Path.Combine(outputDirectory.FullName, deviceOutputFileName), implementation.Device);
+                File.WriteAllText(Path.Combine(outputDirectory.FullName, asyncDeviceOutputFileName), implementation.AsyncDevice);
+            }
             throw;
         }
     }
diff --git a/tests/MetadataSerializerTests.cs b/tests/MetadataSerializerTests.cs
index f5bb566..83f6c2d 100644
--- a/tests/MetadataSerializerTests.cs
+++ b/tests/MetadataSerializerTests.cs
@@ -6,7 +6,7 @@ namespace Harp.Generators.Tests;
 [TestClass]
 public sealed class MetadataSerializerTests
 {
-    DirectoryInfo outputDirectory;
+    DirectoryInfo? outputDirectory;
 
     [TestInitialize]
     public void Initialize()
@@ -51,9 +51,13 @@ public void Metadata_RoundTripSerializes(string metadataFileName, Type type)
         }
         catch (AssertFailedException)
         {
-            outputDirectory.Create();
-            File.WriteAllText(Path.Combine(outputDirectory.FullName, Path.GetFileName(metadataFileName)), roundTripContents);
-            File.WriteAllText(Path.Combine(outputDirectory.FullName, $"{Path.GetFileNameWithoutExtension(metadataFileName)}_orig.yml"), metadataContents);
+            if (outputDirectory is not null)
+            {
+                outputDirectory.Create();
+                var originalMetadataFileName = $"{Path.GetFileNameWithoutExtension(metadataFileName)}_orig.yml";
+                File.WriteAllText(Path.Combine(outputDirectory.FullName, Path.GetFileName(metadataFileName)), roundTripContents);
+                File.WriteAllText(Path.Combine(outputDirectory.FullName, originalMetadataFileName), metadataContents);
+            }
             throw;
         }
     }
diff --git a/tests/PayloadMarshal.cs b/tests/PayloadMarshal.cs
index 83caaa0..e266ab7 100644
--- a/tests/PayloadMarshal.cs
+++ b/tests/PayloadMarshal.cs
@@ -9,13 +9,16 @@ internal static partial class PayloadMarshal
 {
     internal static HarpVersion ReadHarpVersion(ArraySegment<byte> segment)
     {
-        var major = segment.Array[segment.Offset];
-        var minor = segment.Array[segment.Offset + 1];
+        var major = segment.Array?[segment.Offset];
+        var minor = segment.Array?[segment.Offset + 1];
         return new HarpVersion(major, minor);
     }
 
     internal static void Write(ArraySegment<byte> segment, HarpVersion value)
     {
+        if (segment.Array is null)
+            return;
+
         segment.Array[segment.Offset] = (byte)value.Major.GetValueOrDefault();
         segment.Array[segment.Offset + 1] = (byte)value.Minor.GetValueOrDefault();
     }
diff --git a/tests/YamlStream.cs b/tests/YamlStream.cs
index 87e571e..97bcdc7 100644
--- a/tests/YamlStream.cs
+++ b/tests/YamlStream.cs
@@ -55,8 +55,8 @@ internal class YamlSequenceNode : YamlNode
         internal YamlSequenceNode(IParser parser)
         {
             Start = parser.Consume<SequenceStart>();
-            SequenceEnd end;
-            while (!parser.TryConsume(out end))
+            SequenceEnd? end;
+            while (!parser.TryConsume<SequenceEnd>(out end))
             {
                 Children.Add(Parse(parser));
             }
@@ -83,8 +83,8 @@ internal class YamlMappingNode : YamlNode
         internal YamlMappingNode(IParser parser)
         {
             Start = parser.Consume<MappingStart>();
-            MappingEnd end;
-            while (!parser.TryConsume(out end))
+            MappingEnd? end;
+            while (!parser.TryConsume<MappingEnd>(out end))
             {
                 var key = new YamlScalarNode(parser);
                 var value = Parse(parser);
@@ -114,9 +114,9 @@ class YamlScalarNodeEqualityComparer : IEqualityComparer<YamlScalarNode>
         {
             public static readonly YamlScalarNodeEqualityComparer Default = new();
 
-            public bool Equals(YamlScalarNode x, YamlScalarNode y)
+            public bool Equals(YamlScalarNode? x, YamlScalarNode? y)
             {
-                return x.Event.Value == y.Event.Value;
+                return x?.Event.Value == y?.Event.Value;
             }
 
             public int GetHashCode([DisallowNull] YamlScalarNode obj)