ThenKeyOr is not removing the void type

[Blu-J]

Let us have a structure S.
Let a key K might be on structure with partial property P = S[K] \Intersect !void .(For example S = { K?: P })
Let fn be idLens<S>().thenKeyOr('fallback', K).get
We expect fn :: S -> P but get fn :: S -> P \Union void
To solve this I expect that we need subtraction types microsoft/TypeScript#4183