Yii ошибка СMemСache - return this->_cache->get($key);

СMemcache -
php notice:

* @return string the value stored in cache, false if the value is not in the cache or expired.
147      */
148     protected function getValue($key)
149     {
150         return $this->_cache->get($key);
151     }
152 
153     /**
154      * Retrieves mult