Both this ticket and #19094 started from one method in urllib.parse and then generalized a proposal for the rest of the submodule to move away from duck-typing and to instead raise TypeErrors (or at least some error) for invalid types. The attached PR does that. But it broke pip, which was passing None to the `fragment` argument of `urlunsplit()`.

In a blaze of efficiency, Pip already merged my fix, but since the CPython test suite depends on the current version of pip -- perhaps there's an argument for at least raising a deprecation warning for ``None`` and then converting to '' or b''? In any case, green CI makes patches more reviewable, so I'm inclined to add such a warning/conversion for now and then see how feedback goes. Cheers, all.

BTW: perhaps we can close this as dupe of #19094?