Calling shlex.split(None) is deprecated since Python 3.9: commit 975ac32 of bpo-33262.

What's New in Python 3.9:

Passing None as the first argument to the shlex.split() function has been deprecated. (Contributed by Zackery Spytz in bpo-33262.)

IMO it's now time to remove this deprecated feature.

I wrote PR #94353 to implement this change.