public function params(array $keys = array(), $onlyExistingParams = false)
    {
        if(count($keys) == 0)
            return $this->params;

        $params = array();

        foreach($keys as $key) {
            $key = trim($key);

            if($onlyExistingParams && isset($this->params[$key]))
                $params[$key] = $this->params[$key];
            else
                $params[$key] = isset($this->params[$key]) ? $this->params[$key] : null;
        }

        return $params;
    }