def check_for_update_type(files):
    """Check to see if a set only update is needed.

    Parameters
    ----------
    cf : Config
    files : Dict[name : contents]
        name : str
            is the name of a file to be used
        contents : str
             is the nft commands to be output

    Returns
    -------
    bool or List[str]
        None if update not needed, or otherwise
        return an array of the lists that need to be changed
    """

    if 'incoming.nft' in files \
       or 'outgoing.nft' in files:
        return None

    ret = None
    for li in ['whitelist', 'blacklist', 'blacknets']:
        # if the rules have changed
        # full install needed
        if li+'.nft' in files:
            return None
        if li+'_sets.nft' in files:
            if ret is None:
                ret = [li]
            else:
                ret += [li]
    return ret