return type of UserDefinedFunction is not defined

[vforchi]

I developed some custom functions by implementing UserDefinedFunction. One of these functions returns a Timestamp (a DATE in the signature), but when it is in one of the return columns the DBType is null. I think this is because the ADQL parser only considers instances of DefaultUDF and not of UserDefinedFunction. I can't extend DefaultUDF, because it's final.

I can't easily get rid of the custom classes for each function, because I rely this in other parts of the code, is there any other way around it?