def prepare_private_target_groups(self, review_request):
        queryset = review_request.target_groups.filter(invite_only=True)

        return list(queryset.values_list('pk', flat=True)) or [0]
KDF from RFC7292 appendix b.2 - https://tools.ietf.org/html/rfc7292#page-19
dataset/ETHPy150Open reviewboard/reviewboard/reviewboard/reviews/search_indexes.py/ReviewRequestIndex.prepare_private_target_groups--crossover with--dataset/ETHPy150Open wbond/oscrypto/oscrypto/_pkcs12.py/pkcs12_kdf