I have no idea why, but asserting that each value added to emptydirs is not
None didn't fix this:
File "/mnt/c/Users/Matt/hg/mercurial/hgweb/webcommands.py", line 621, in dirlist:
Function bytes.join was called with the wrong arguments [wrong-arg-types]
Expected: (self, iterable: Iterable[bytes])
Actually passed: (self, iterable: List[None])