public static function load($id, $persistenceFacade, $session) {
    // get state from session
    $state = $session->get($id);
    if ($state == null) {
      return null;
    }
    // create instance
    $instance = new PersistentIterator($id, $persistenceFacade, $session,
            $state['currentOID']);
    $instance->end = $state['end'];
    $instance->oidList = $state['oidList'];
    $instance->processedOidList = $state['processedOidList'];
    $instance->currentDepth = $state['currentDepth'];
    $instance->aggregationKinds = $state['aggregationKinds'];
    return $instance;
  }