QVT14 — QVTr: overriding create nothing

An overriding relation may need to create nothing when the derived input pattern does not need transformation by the polymorphism. It might be transformed elsewhere explicitly. (Concrete example is OclType in the ATL metamodel which is defined as a derived OclExpression in ATL but not in OCL.)

Create nothing could be achieved by omitting the engforced domain but that violates a consistent overrideing domains WFR.

Create nothing is more sensibly achieved by no output patterns in the enforced domain,