Seems it's the same functionality as #13, but more polished here. I like the AllowNull attribute to explicitely enable the nil non-standard feature.

Seems it's the same functionality as #13, but more polished here. I like the AllowNull attribute to explicitely enable the nil non-standard feature.

Python implementation has this approach as well, and I like that this non-standard feature is not enabled by default too.
This is different from #13 as #13 is about deserializing response data which have NULL values. This (#11) allows to send NULL values as parameters of method in the XML-RPC request.
However, I thing #13 could be more polished if deserialization would take XmlRpcMissingMapping(MappingAction.Ignore) attribute into account for data deserialization. For example:

public class MyResult
{
    public string propertyOne;
    [XmlRpcMissingMapping(MappingAction.Ignore)] // don't care if server don't return this field
    public string propertyTwo;
}

Solution could allow NULL (<nil/>) for propertyTwo but does not allow NULL for propertyOne and rise exception as in standard behavior. Of course, if I understand the project correctly.

Should this be closed?