def set_is_singles(slots):
    """Check whether a set is in the singles or doubles format based on its slots"""
    if slots is None:
        return False
    for slot in slots:
        entrant = slot['entrant']
        try:
            participants = entrant['participants']
            if len(participants) > 1:
                return False
            else:
                return True
        except KeyError:
            return True