Each restriction at the language level adds a cost. The cost of having simple nullable types like you do in Java or C# is worth it. The cost of trying to formalize away null errors isn't. That is what I think. Just because you can do something doesn't mean that you should, so just because you can ensure no errors of class X happens at a language level doesn't mean that enforcing that at a language level is the best solution.

> It's not possible to solve problems at the code level. That would require every single developer writing in that language to account for all the holes in the type systems.

I'm not sure what you mean with this. Of course you can fix this at a code level. Not for the entire world of course, but you can do it in the code you write.