[NullGuard] Return value of property 'TCode.r2rml4net.Log.LogFacadeBase TCode.r2rml4net.TriplesGeneration.MapProcessorBase::Log()' is null.

[A7medDaoud]

I have got that exception "[NullGuard] Return value of property 'TCode.r2rml4net.Log.LogFacadeBase TCode.r2rml4net.TriplesGeneration.MapProcessorBase::Log()' is null." when dumping the example here https://www.w3.org/TR/r2rml/#dfn-r2rml-view
with a mapping file attached below
it works without the join between the EMP table and the DEPT table, but when perform the join i got that exception.
mapping.txt