code: public function has($userId, $callId)
      {
          $key = $this->getCacheKey($userId, $callId);
          if (!isset($this->cache[$key])) {
              return $this->getStorage()->has($userId, $callId);
          }
          return $this->exists($key);
      }
docs: Whenever or not a dataset exists.
  
  @param string $userId
  @param string $callId
  @return boolean