def METHOD_NAME(self,
                 filename: Union[str, Path],
                 add: bool = True) -> Optional[AudioFile]:
    """Add a song to the library based on filename.
    If 'add' is true, the song will be added and the 'added' signal
    may be fired.
    Example (add=False):
        load many songs and call Library.add(songs) to add all in one go.
    The song is returned if it is in the library after this call.
    Otherwise, None is returned.
    """
    key = normalize_path(filename, True)
    song = None
    if key not in self._contents:
        song = MusicFile(filename)
        if song and add:
            self.add([song])
    else:
        print_d(f"Already got file {filename!r}")
        song = self._contents[key]
    return song