def _get_contacts_from_cache(cache=None):
    """
    :param cache: Cache to check for contacts. If None, returns None.
    :type cache: src.rapid_pro_to_engagement_db.cache.RapidProSyncCache | None
    :return: Contacts from a cache, if the cache exists and a previous contacts file exists in the cache, else None.
    :rtype: list of temba_client.v2.Contact | None
    """
    if cache is None:
        return None
    else:
        return cache.get_contacts()