[451724] Improve resilience to null model elements
[451224] Additional *.oclas validation tests
[451224] Change OpaqueExpression.expressionInOCL to non-containment
[451224] Add Sample Reflective Ecore Editor test
[451369] Use a TransientASResource for independent ExpressionInOCL
parsing
[unrelated] Pass ExpressionInOCL errors to outer resource