git p4 sync: "str expected, not %s"

[Massimo B.]

Hello everybody,

since last updates, git p4 does not work anymore:

# git p4 sync --verbose
Reading pipe: ['git', '--git-dir', 
'/mnt/data/userspace/project-pb/MM6.test/.git', 'rev-parse', '--git-dir']
Reading pipe: git rev-parse --git-dir
Reading pipe: git rev-parse --show-cdup
Reading pipe: ['git', '--git-dir', b'.', 'rev-parse', '--git-dir']
Traceback (most recent call last):
  File "/usr/libexec/git-core/git-p4", line 4163, in <module>
    main()
  File "/usr/libexec/git-core/git-p4", line 4155, in main
    os.environ["GIT_DIR"] = cmd.gitdir
  File "/usr/lib64/python3.6/os.py", line 674, in __setitem__
    value = self.encodevalue(value)
  File "/usr/lib64/python3.6/os.py", line 744, in encode
    raise TypeError("str expected, not %s" % type(value).__name__)
TypeError: str expected, not bytes

git version 2.22.0
Gentoo Linux
Global Python is 3.6.

Last working version I found: 2.20.1

Best regards,
Massimo