code: public function type($key)
      {
          if (!$this->storage->hasKey($key)) {
              return 'none';
          }
  
          $value = $this->storage->get($key);
          if (is_string($value)) {
              return 'string';
          } elseif ($value instanceof \SplDoublyLinkedList) {
              return 'list';
          } else {
              throw new UnexpectedValueException('Unknown datatype encountered');
          }
      }
docs: StatusReply