code: public JvmOperation findOverriddenOperation(JvmOperation operation) {
  		if (operation.getVisibility() == JvmVisibility.PRIVATE) {
  			return null;
  		}
  		ITypeReferenceOwner owner = new StandardTypeReferenceOwner(services, operation.eResource().getResourceSet());
  		LightweightTypeReference declaringType = owner.toLightweightTypeReference(operation.getDeclaringType());
  		TypeParameterSubstitutor<?> substitutor = createSubstitutor(owner, declaringType);
  		return findOverriddenOperation(operation, declaringType, substitutor, owner, new ContextualVisibilityHelper(visibilityHelper, declaringType));
  	}
docs: /* @Nullable