And AI code reviews encourage overly delusional defensive paranoia. triple null checking deep inside a function is technically a real risk, but in practice should never be hit because you've checked for nulls in every function that calls or could call the function in question and is thus not necessarily worth guarding against.

Are LLMs too dumb to understand the type system? Or is the type system too bad, to represent non-nullable?

Even in Python with its meh-ish optional typing system something that can be None is different from something that cannot be None.