Oh sure, yeah I see how #4 would be useful. Generally I've used / seen `undefined` used for that in the past, which can be problematic because it might mean wha

Oh sure, yeah I see how #4 would be useful. Generally I've used / seen `undefined` used for that in the past, which can be problematic because it might mean what you think it means, or it might mean something broken in your algo by mistake.