protected function registerProxyObject(ObjectID $umi, PersistentObject $obj, $buildDepth) {
    $oid = $obj->getOID();
    if (strlen($oid->getPrefix()) > 0) {
      self::$logger->debug("NOT A PROXY");
      return;
    }
    $this->registerObject($umi, $obj, $buildDepth, self::PROXY_OBJECTS_SESSION_VARNAME);
  }