Null serialization creates <Null /> node ignoring property name instead of using xsi:nil="true"

When serializing property with null value, the serializer creates <Null xmlns="https://extendedxmlserializer.github.io/v2"/> node ignoring the property name.

Example output:

<?xml version="1.0" encoding="utf-8"?>
<ClassWithString xmlns="clr-namespace:ExtendedXmlSerializer.Tests.ReportedIssues;assembly=ExtendedXmlSerializer.Tests">
   <Null xmlns="https://extendedxmlserializer.github.io/v2" />
</ClassWithString>

Repro:

var config = new ConfigurationContainer();
config.Emit(EmitBehaviors.Always);
var serializer = config.Create();
string xml = serializer.Serialize(new ClassWithString());

public class ClassWithString
{
    public string Name { get; set; }
}

This leads us to situation where serializer does not preserve the null value if there is custom default value defined, even if it`s being forced to serialize it.

        [Fact]
        public void ShouldPreserveNullValueIfDefaultIsNotNull()
        {
            var config = new ConfigurationContainer();
            config.Emit(EmitBehaviors.Always); //no matter what
            var serializer = config.Create();

            string xml = serializer.Serialize(new ClassWithDefautString() { Name = null });
            var deserialized = serializer.Deserialize<ClassWithDefautString>(xml);

            deserialized.Name.Should().BeNull();    //fail
        }

        public class ClassWithDefautString
        {
            public string Name { get; set; } = "Unnamed";
        }

Newtonsoft.Json handles this using null keyword which has no equivalent in XML. I hope it could be emulated using syntax like <Name xsi:nil="true"/> or <Name><Null xmlns="https://extendedxmlserializer.github.io/v2"/></Name>. The issue will probably span to all reference types. I have no idea how nulls could be handled in attributes.

My particular use case is serialization of config objects that have default values for all the properties. I would want to skip unchanged ones for sake of readability, however saving explicit nulls is not preserved.

BTW: I would like to thank all the authors for their great job! This is the most feature rich XML serializer on the market 😃

[WojciechNagorski]

@Mike-EEE We can release v2.1 today, but I need release notes. Could you prepare it?

[Leszek-Kowalski]

Happy Thanksgiving! Actually we don`t celebrate it in Europe in Poland 😃 Do not rush. Thanksgiving is a time for family, not coding.