/**
  * {@inheritdoc}
  */
 protected function extract(Message $message)
 {
     if (!$message->hasKeys()) {
         return null;
     }
     return new ArrayIterator($message->keys);
 }
 /**
  * {@inheritdoc}
  */
 protected function extract(Message $message)
 {
     if ($message->hasResults()) {
         return $this->iteratorFromResults($message->results);
     }
     if ($message->hasKeys()) {
         return $this->iteratorFromKeys($message->keys);
     }
     return null;
 }