def find_backend(line: str) -> Optional[str]:
    """
    Find one (or multiple) backend in a code line of the init.

    Args:
        line (`str`): A code line of the main init.

    Returns:
        Optional[`str`]: If one (or several) backend is found, returns it. In the case of multiple backends (the line
        contains `if is_xxx_available() and `is_yyy_available()`) returns all backends joined on `_and_` (so
        `xxx_and_yyy` for instance).
    """
    if _re_test_backend.search(line) is None:
        return None
    backends = [b[0] for b in _re_backend.findall(line)]
    backends.sort()
    return "_and_".join(backends)

    Find one (or multiple) backend in a code line of the init.

    Args:
        line (`str`): A code line of the main init.

    Returns:
        Optional[`str`]: If one (or several) backend is found, returns it. In the case of multiple backends (the line
        contains `if is_xxx_available() and `is_yyy_available()`) returns all backends joined on `_and_` (so
        `xxx_and_yyy` for instance).
    
dpkd/transformers/utils/check_inits.py