def get_list_id(list_name, alexa_lists):
    """Find a list id for the corresponding list name. 
    If none is found, return None."""
    # type: (str, list) -> Union[str, None]

    for alexa_list in alexa_lists:
        if alexa_list.name == list_name:
            return alexa_list.list_id
    
    return None