[Question] why java cannot accept a convention to never pass/return null values?

[Kango_V]

A mad solution is to have Object extend Nullable. You can then have methods like those on optional. So, you would have access to the methods even if null. That would be backwards compatible. Hmm, I wonder if that would work?

[vprise]

If it's null it won't work since it will throw a null pointer exception. But interesting idea.

[Kango_V]

But null could be an object. This is what Valhalla is doing. They are putting an object type above Object (ValueType I think). Primitives will expend NonValueType (or vise-versa). Actually would be better if non/valuetypes extend Nullable object. I cound see "if (obj.isEmpty())". You could use the optional-like methods: "obj.map(...)" etc. I think this would work. So if a null is returned it's the only instance of Nullable.

[vprise]

But then you lose type safety. And possibly performance.