def has_refseq(db_list):
    """
    Return the index of the list where the 'RefSeq' string is located.
    Otherwise return None
    :param db_list: A list of db names taken as the first element of the tuples in a
    Swissprot.record.cross_references list
    :return: int: index or None
    """
    if 'RefSeq' in db_list:
        return db_list.index('RefSeq')
    else:
        return None