def list_tester(user_list, session_list, watch_lists):
    """
    :param user_list: The user list if they supplied one
    :param session_list: The session attributes or persistent attributes
    :param watch_lists: tuple of watch list aliases
    :return: True if list is a custom list, False if watchlist
    """
    try:
        session_list['list']
    except KeyError:
        session_list['list'] = None
    if user_list is None and session_list['list'] is None:
        return True
    if not user_list and not session_list['list']:
        return True
    if user_list.lower() in watch_lists:
        return True
    return False