def get_subdirectory(cls, location):
        """
        Return the path to setup.py, relative to the repo root.
        Return None if setup.py is in the repo root.
        """
        # find the repo root
        git_dir = cls.run_command(
            ['rev-parse', '--git-dir'],
            show_stdout=False,
            stdout_only=True,
            cwd=location,
        ).strip()
        if not os.path.isabs(git_dir):
            git_dir = os.path.join(location, git_dir)
        repo_root = os.path.abspath(os.path.join(git_dir, '..'))
        return find_path_to_setup_from_repo_root(location, repo_root)