Maybe spit warnings when undefined is used? In the same way it does for when you use typeScript in a type-loose way.
replyBut yeah it's a fair point. Sometimes I think I should just write my own lang (a subset of typescript), in the same fashion that Lisette dev has done.
You can already do this with strict type checking enabled and the NonNullable type.
replyYou can't enforce it in any normal codebase because null is used extensively in the third party libraries you'll have to use for most projects.