docs: public ResponseWrapper addOrRemoveCrossGroupMembers(long gid, CrossGroup[] groups)
              throws APIConnectionException, APIRequestException {
          CrossGroupPayload payload = new CrossGroupPayload.Builder()
                  .setCrossGroups(groups)
                  .build();
          Preconditions.checkArgument(0 != gid, "gid should not be empty");
          Preconditions.checkArgument(null != payload, "CrossGroup must not be null");
          return _httpClient.sendPost(_baseUrl + crossGroupPath + "/" + gid + "/members", payload.toString());
      }