If you rely on any frameworks or libraries whatsoever, you can't assume they aren't using null in this way and would break if the language spec changed. The only common ground you and those developers have is the language specification's rules.

(If you actually do roll all your JS by hand in house, congratulations and I'm impressed, but (a) that's a minority position in any house that has to do professional JavaScript and (b) oh wow you're reinventing a lot of wheels).