protected function _key($key)
    {
        $key = $this->key($key);
        if ($key === false) {
            throw new InvalidArgumentException('An empty value is not valid as a cache key');
        }

        return $this->_config['prefix'] . $key;
    }
protected function _key($key)
    {
        $key = $this->key($key);
        if ($key === false) {
            throw new InvalidArgumentException('An empty value is not valid as a cache key');
        }

        return $this->_config['prefix'] . $key;
    }
protected function _key ( $ key ) { $ key = $ this -> key ( $ key ) ; if ( $ key === false ) { throw new InvalidArgumentException ( 'An empty value is not valid as a cache key' ) ; } return $ this -> _config [ 'prefix' ] . $ key ; }
Generates a safe key, taking account of the configured key prefix

@param string $key the key passed over
@return mixed string $key or false
@throws \InvalidArgumentException If key's value is empty
Generates a safe key taking account of the configured key prefix