protected function makeUmis($oids, $umiPrefix) {
    $result = [];
    foreach ($oids as $oid) {
      if (strlen($oid->getPrefix()) == 0) {
        $umi = new ObjectId($oid->getType(), $oid->getId(), $umiPrefix);
        $result[] = $umi;
      }
    }
    return $result;
  }