Welcome to any of my codebases. Undefined and null have clear semantic differences, and those differences are important to the function, safety, and performance of the code.
That's perfectly fine. If you need to distinguish between them, then you should do that. There's plenty of code that's different though. I would say probably most of it.
The semantic differences seem to be local at best. In any case, there's plenty of code that legitimately doesn't concern itself with any of that.
