Result of os.path.realpath("") is incorrect if cwd is on letter-less drive (\\?\-prefixed)

Bug report

1. Create volume, dir on it, don't assign a drive letter
2. In Python:

>>> import os
>>> os.chdir("\\\\?\\Volume{<uuid>}\\<dir>")
>>> os.path.realpath("")
'\\\\?\\Volume{<uuid>}\\<dir>\\.'

The dot is invalid in \\?\-prefixed path.
Dots (. and ..) are normalized by Windows API (at least on NTFS). But \\?\ paths bypass normalization and so may not contain dots. See, for example, here.
All later WinAPI calls with this path fail.

As a simple test, dir \\?\Volume{<uuid>}\dir\. doesn't work whereas dir \\?\Volume{<uuid>}\dir works.

P.S. os.path.realpath(".") gives the same invalid result

Your environment

CPython 3.10.0
Windows 10

Context
The problem arises from pip.
sys.path contains empty string (meaning current dir I presume).
And legacy installation method resolves sys.path relatively to cwd.

Investigation
Here:
https://github.com/python/cpython/blob/4bed0db7c222f8df1b4e31107c0305214caf3f56/Lib/ntpath.py#L704
os.path.join still adds slash even if the second argument is empty. And if the path is ended with slash, dot is added somewhere below.

I fixed it to:

path = cwd if path == "." or path == "" else join(cwd, path)

Comienza en Lib/ntpath.py alrededor de la línea 704 mencionada y reproduce el comportamiento de Windows con una ruta de volumen \?-prefijada cuyo directorio actual no tiene letra de unidad. Comprueba cómo os.path.realpath("") y os.path.realpath(".") construyen sus rutas y, después, añade cobertura de regresión que muestre que ninguno de los resultados termina con un componente \. no válido y que la ruta resultante funciona con llamadas posteriores a WinAPI.