DMN QName regex does not match with serialization strategy.

A qname string serialization as

{http://namespace}localPart

would fail the regex of MarshallingUtils.

Additionally FunctionDefinition could now rely on the additionalAttributes generally available at the level of DMNModelInstrumentedBase (which would also serialize any other type of additional attributes, preserving from any original .dmn file).

Finally, it was noted calling getDecisionResultByName on DMNResultImpl by passing a wrong name would have thrown the stacktrace for wrong use of Optional.get(), instead of returning null as per getDecisionResultById() of the same class.