def METHOD_NAME(self) -> Optional[str]:
    """
    Returns the cursor value.
    Files are synced in order of last-modified with secondary sort on filename, so the cursor value is
    a string joining the last-modified timestamp of the last synced file and the name of the file.
    """
    if self._file_to_datetime_history.items():
        filename, timestamp = max(self._file_to_datetime_history.items(), key=lambda x: (x[1], x[0]))
        return f"{timestamp}_{filename}"
    return None