Is there anything else we can use to indicate that the PortModel is associated to a statement that does not have an assignment? For one thing string comparisons are very unreliable (which is why we prefer enum whenever possible). Is there any other way to determine that? Maybe through **Statement** instances you have internally? Relying on tool-tip is likely to be broken, say, when they decide to show "result value" in the tool-tip. Then that will break your stuff.