XSD Validation throws an exception when self-closing tag used

[nataliaheliova]

I came across an issue in .NET Core 2.1 when validating an XML containing self-closing tag.

I have a model with property Value of generic type T:

[XmlInclude(typeof(Parameter<string>))]
public class Parameter
{
    [XmlAttribute]
    public string Name { get; set; }
}
public class Parameter<T> : Parameter
{
     public T Value { get; set; }
}

The corresponding XSD Schema snippet:

<xs:complexType name="parameter">
  <xs:attribute type="xs:string" name="Name" use="required" />
</xs:complexType>

<xs:complexType name="stringParameter">
  <xs:complexContent>
    <xs:extension base="parameter">
      <xs:sequence>
        <xs:element name="Value" minOccurs="0" maxOccurs="1"/>
      </xs:sequence>
    </xs:extension>
  </xs:complexContent>
</xs:complexType>

Both the model and schema are part of a project targeting .NET Standard 2.0.

Then I created test project targeting .NET Core 2.1 and .NET Framework 4.6.1 where I am trying to validate (and deserialize) XML containing following lines:

<Parameters>
    <Parameter xsi:type="stringParameter" Name="SomeName">
        <Value />
     </Parameter>
</Parameters>

.NET Framework 4.6.1 does not have any issue (XML is evaluated as valid and is sucessfully deserialized). Validation under .NET Core 2.1 fails (by which I do NOT mean that as a result the XML is invalid, the validation process just crashes) and throws the following exception:

System.InvalidOperationException: There is an error in XML document (1, 226). ---> System.ArgumentNullException: Value cannot be null.
Parameter name: value
    at System.Xml.Schema.XmlUntypedConverter.ToString(Object value, IXmlNamespaceResolver nsResolver)
   at System.Xml.Schema.XmlBaseConverter.ToString(Object value)
   at System.Xml.XsdValidatingReader.ReadElementContentAsString()
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderRootClass.Read2_ParameterOfString(Boolean isNullable, Boolean checkType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderRootClass.Read3_Parameter(Boolean isNullable, Boolean checkType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderRootClass.Read4_RootClass(Boolean isNullable, Boolean checkType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderRootClass.Read5_RootClass()
--- End of inner exception stack trace ---
    at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
   at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader)

I could find two workarounds to make it work:
1.) In XML, replace <Value /> with <Value></Value>
or 2.) In XSD, add type="xs:string" to element Value

But still, it is strange, isn't it?

Small example with both schemas:
Serializer.zip

Operating system: Windows 10 1803
IDE: Visual Studio 2017 15.9.6

Thanks,
Natalia

[krwq]

cc: @huanwu, @Lxiamail, @zhenlan - this is most likely serialization bug but if it happens to not be one could you please help isolating the repro to not use generated assembly?

[danmoseley]

@nataliaheliova can you please let us know whether this still happens in 3.0 preview 3? Even if you must use 2.1, that information may help us investigate.

[nataliaheliova]

We just tried it out together with @jakubsturc and we can confirm that we get the same exception in 3.0 preview 3.