🐛 fix DefaultValue suppression for nullable reference-type properties

src/Directory.Packages.props

@@ -8,8 +8,8 @@
     <PackageVersion Include="MinVer" Version="6.0.0" />
 
     <!-- Generator dependencies -->
-    <PackageVersion Include="XmlSchemaClassGenerator-beta" Version="99.0.8-local" />
-    <PackageVersion Include="XmlSchemaClassGenerator.Analyzer" Version="99.0.8-local" />
+    <PackageVersion Include="XmlSchemaClassGenerator-beta" Version="99.0.9-local" />
+    <PackageVersion Include="XmlSchemaClassGenerator.Analyzer" Version="99.0.9-local" />
     <PackageVersion Include="System.CommandLine" Version="2.0.2" />
 
     <!-- Test dependencies -->

src/netex/Spillgebees.NeTEx.Models.Tests/Serialization/NetexSerializationTests.cs

@@ -157,8 +157,6 @@ public void Should_serialize_and_deserialize_parking_with_typed_enum_list()
         deserialized.ParkingPaymentProcess[1].Should().Be(ParkingPaymentProcessEnumeration.PayByMobileDevice);
     }
 
-
-
     [Test]
     public void Should_serialize_and_deserialize_optional_element_with_default_value_to_nullable_property_with_fallback_default()
     {
@@ -267,4 +265,65 @@ public void Should_have_xml_root_attribute_on_publication_delivery_structure()
         xmlRootAttr.ElementName.Should().Be("PublicationDelivery");
         xmlRootAttr.Namespace.Should().Be("http://www.netex.org.uk/netex");
     }
+
+    /// <summary>
+    /// PublicationDeliveryStructure.Version defaults to "1.0" via backing field initialization.
+    /// With <c>[DefaultValueAttribute]</c> suppressed on <c>string?</c> properties,
+    /// <c>XmlSerializer</c> must include the default value in the serialized XML.
+    /// </summary>
+    [Test]
+    public void Should_serialize_default_string_value_when_property_is_left_as_default()
+    {
+        // arrange
+        var serializer = new XmlSerializer(typeof(PublicationDeliveryStructure));
+        var original = new PublicationDeliveryStructure
+        {
+            PublicationTimestamp = DateTimeOffset.UtcNow,
+            ParticipantRef = "test",
+        };
+
+        // act
+        using var writer = new StringWriter();
+        serializer.Serialize(writer, original);
+        var xml = writer.ToString();
+
+        using var reader = new StringReader(xml);
+        var deserialized = serializer.Deserialize(reader) as PublicationDeliveryStructure;
+
+        // assert
+        xml.Should().Contain("version=\"1.0\"");
+        deserialized.Should().NotBeNull();
+        deserialized.Version.Should().Be("1.0");
+    }
+
+    /// <summary>
+    /// Even when PublicationDeliveryStructure.Version is explicitly set to the default value of "1.0",
+    /// it should still be serialized in the XML since the [DefaultValue] attribute is suppressed on nullable string
+    /// properties to avoid unintended consequences of the serializer omitting elements with default values.
+    /// </summary>
+    [Test]
+    public void Should_serialize_default_string_value_when_property_is_explicitly_set_to_default()
+    {
+        // arrange
+        var serializer = new XmlSerializer(typeof(PublicationDeliveryStructure));
+        var original = new PublicationDeliveryStructure
+        {
+            PublicationTimestamp = DateTimeOffset.UtcNow,
+            ParticipantRef = "test",
+            Version = "1.0",
+        };
+
+        // act
+        using var writer = new StringWriter();
+        serializer.Serialize(writer, original);
+        var xml = writer.ToString();
+
+        using var reader = new StringReader(xml);
+        var deserialized = serializer.Deserialize(reader) as PublicationDeliveryStructure;
+
+        // assert
+        xml.Should().Contain("version=\"1.0\"");
+        deserialized.Should().NotBeNull();
+        deserialized.Version.Should().Be("1.0");
+    }
 }

src/netex/Spillgebees.NeTEx.Models.Tests/XsdTypeMappingTests.cs

@@ -104,7 +104,7 @@ public void Should_generate_default_value_for_xsd_default_version_attribute()
     }
 
     [Test]
-    public void Should_have_default_value_attribute_on_version_property()
+    public void Should_not_have_default_value_attribute_on_nullable_string_property_with_xsd_default()
     {
         // arrange
         var property = typeof(PublicationDeliveryStructure)
@@ -113,9 +113,23 @@ public void Should_have_default_value_attribute_on_version_property()
         // act
         var attr = property.GetCustomAttribute<DefaultValueAttribute>();
 
+        // assert
+        attr.Should().BeNull();
+    }
+
+    [Test]
+    public void Should_still_have_default_value_attribute_on_value_type_property_with_xsd_default()
+    {
+        // arrange
+        var property = typeof(DayTypeAssignmentVersionStructure)
+            .GetProperty(nameof(DayTypeAssignmentVersionStructure.IsAvailable))!;
+
+        // act
+        var attr = property.GetCustomAttribute<DefaultValueAttribute>();
+
         // assert
         attr.Should().NotBeNull();
-        attr!.Value.Should().Be("1.0");
+        attr!.Value.Should().Be(true);
     }
 
     [Test]

src/siri/Spillgebees.SIRI.Models.Tests/Serialization/SiriSerializationTests.cs

@@ -152,4 +152,54 @@ public void Should_have_correct_xml_type_namespace_on_siri_types()
         xmlTypeAttr.Should().NotBeNull();
         xmlTypeAttr.Namespace.Should().Be("http://www.siri.org.uk/siri");
     }
+
+    /// <summary>
+    /// Siri.Version defaults to "2.1" via backing field initialization.
+    /// With <c>[DefaultValueAttribute]</c> suppressed on <c>string?</c> properties,
+    /// <c>XmlSerializer</c> must include the default value in the serialized XML.
+    /// </summary>
+    [Test]
+    public void Should_serialize_default_string_value_when_property_is_left_as_default()
+    {
+        // arrange
+        var serializer = new XmlSerializer(typeof(Siri));
+        var original = new Siri();
+
+        // act
+        using var writer = new StringWriter();
+        serializer.Serialize(writer, original);
+        var xml = writer.ToString();
+
+        using var reader = new StringReader(xml);
+        var deserialized = serializer.Deserialize(reader) as Siri;
+
+        // assert
+        xml.Should().Contain("version=\"2.1\"");
+        deserialized.Should().NotBeNull();
+        deserialized.Version.Should().Be("2.1");
+    }
+
+    /// <summary>
+    /// Even when Siri.Version is explicitly set to the default value of "2.1", it should still be serialized in the XML since the [DefaultValue] attribute is suppressed on nullable string properties to avoid unintended consequences of the serializer omitting elements with default values.
+    /// </summary>
+    [Test]
+    public void Should_serialize_default_string_value_when_property_is_explicitly_set_to_default()
+    {
+        // arrange — explicitly setting Version to the same value as the XSD default
+        var serializer = new XmlSerializer(typeof(Siri));
+        var original = new Siri { Version = "2.1" };
+
+        // act
+        using var writer = new StringWriter();
+        serializer.Serialize(writer, original);
+        var xml = writer.ToString();
+
+        using var reader = new StringReader(xml);
+        var deserialized = serializer.Deserialize(reader) as Siri;
+
+        // assert
+        xml.Should().Contain("version=\"2.1\"");
+        deserialized.Should().NotBeNull();
+        deserialized.Version.Should().Be("2.1");
+    }
 }

src/siri/Spillgebees.SIRI.Models.Tests/XsdTypeMappingTests.cs

@@ -96,7 +96,7 @@ public void Should_generate_default_value_for_xsd_default_version_attribute()
     }
 
     [Test]
-    public void Should_have_default_value_attribute_on_siri_version_property()
+    public void Should_not_have_default_value_attribute_on_nullable_string_property_with_xsd_default()
     {
         // arrange
         var property = typeof(Siri)
@@ -105,9 +105,23 @@ public void Should_have_default_value_attribute_on_siri_version_property()
         // act
         var attr = property.GetCustomAttribute<DefaultValueAttribute>();
 
+        // assert
+        attr.Should().BeNull();
+    }
+
+    [Test]
+    public void Should_still_have_default_value_attribute_on_value_type_property_with_xsd_default()
+    {
+        // arrange
+        var property = typeof(HalfOpenTimestampOutputRangeStructure)
+            .GetProperty(nameof(HalfOpenTimestampOutputRangeStructure.EndTimeStatus))!;
+
+        // act
+        var attr = property.GetCustomAttribute<DefaultValueAttribute>();
+
         // assert
         attr.Should().NotBeNull();
-        attr!.Value.Should().Be("2.1");
+        attr!.Value.Should().Be(EndTimeStatusEnumeration.Undefined);
     }
 
     [Test]
@@ -124,21 +138,6 @@ public void Should_generate_default_value_for_xsd_default_enum_property()
         range.EndTimeStatus.Should().Be(EndTimeStatusEnumeration.Undefined);
     }
 
-    [Test]
-    public void Should_have_default_value_attribute_on_enum_property()
-    {
-        // arrange
-        var property = typeof(HalfOpenTimestampOutputRangeStructure)
-            .GetProperty(nameof(HalfOpenTimestampOutputRangeStructure.EndTimeStatus))!;
-
-        // act
-        var attr = property.GetCustomAttribute<DefaultValueAttribute>();
-
-        // assert
-        attr.Should().NotBeNull();
-        attr!.Value.Should().Be(EndTimeStatusEnumeration.Undefined);
-    }
-
     [Test]
     public void Should_use_init_setter_on_collection_properties()
     {