Locate and return the default config for current revison.

def find_config(revision):
    """Locate and return the default config for current revison."""
    if not is_git_repo():
        return None

    cfg_path = f"{revision}:.cherry_picker.toml"
    cmd = "git", "cat-file", "-t", cfg_path

    try:
        output = subprocess.check_output(cmd, stderr=subprocess.STDOUT)
        path_type = output.strip().decode("utf-8")
        return cfg_path if path_type == "blob" else None
    except subprocess.CalledProcessError:
        return None