Model:
	greetings+=Greeting*
	byes+=Bye*;
	
Greeting:
	'Hello' name=ID honest?='!'?;
	
Bye:
	'Bye' greeting=[Greeting]
;

	public void completeBye_Greeting(EObject model, Assignment assignment, ContentAssistContext context, ICompletionProposalAcceptor acceptor) {
		lookupCrossReference(model, FooDslPackage.Literals.BYE__GREETING, acceptor, e -> {
			Greeting greeting = (Greeting) e.getEObjectOrProxy();
			// greeting.name is also null, honest always false if placed in another file
			return greeting.isHonest();
		}, getProposalFactory("ID", context));
	}