public function __isset($name) {
    if ($this->isASleepingReference) {
      $this->referenceWake();
    }
    if ($name === 'guid'
        || $name === 'cdate'
        || $name === 'mdate'
        || $name === 'tags'
      ) {
      return isset($this->$name);
    }
    // Unserialize.
    if (isset($this->sdata[$name])) {
      $this->data[$name] = unserialize($this->sdata[$name]);
      unset($this->sdata[$name]);
    }
    return isset($this->data[$name]);
  }