ST6RI-938 Fix NPE on InstantiationExpression.instantiatedType

[adaussy]

Calling "instantiatedType" on an "InstantiationExpression" with its missing require membership causes an NPE

Calling "instantiatedType" on an "InstantiationExpression" might end up in a NullPointException with the "InstantiationExpression" missing its required "Membership".

Exception in thread "main" java.lang.NullPointerException
	at java.base/java.util.Objects.requireNonNull(Objects.java:233)
	at java.base/java.util.Optional.of(Optional.java:113)
	at java.base/java.util.stream.FindOps$FindSink$OfRef.get(FindOps.java:194)
	at java.base/java.util.stream.FindOps$FindSink$OfRef.get(FindOps.java:191)
	at java.base/java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:150)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:647)
	at org.omg.sysml.delegate.invocation.InstantiationExpression_instantiatedType_InvocationDelegate.dynamicInvoke(InstantiationExpression_instantiatedType_InvocationDelegate.java:47)

This case can happen in an invalid model, however nevertheless the state of the model the application should not fail in an NullPointerException.

[seidewitz]

Thank you for your contribution. However, I am afraid that we cannot accept pull requests at this time from outside the OMG Systems Modeling Community Reference Implementation Working Group development team.

[adaussy]

I was about to provide a JUnit test for this PR but as it is closed now I'm not able push a new version.

If you reopen it, i would gladly provide it.