public function sscan($key, &$iterator, $pattern = null, $count = null)
    {
        if ((string)$iterator === '0') {
            return null;
        }
        $this->init();
        if ($this->actualDriver() === self::DRIVER_PREDIS) {
            $returned = $this->driver->sscan($key, $iterator, ['match' => $pattern, 'count' => $count]);
            $iterator = $returned[0];
            return $returned[1];
        }
        return $this->driver->sscan($key, $iterator, $pattern, $count);
    }