protected function getCustomUrl(array $urlParameters = array())
    {
        $urlParameters = $this->addRequestVariablesToUrlParameters($urlParameters);

        if ($this->customUrl && count($urlParameters) > 0)
        {
            $params = http_build_query($urlParameters);

            if ('' != parse_url($this->customUrl, PHP_URL_QUERY))
            {
                // existing query string, append
                return $this->customUrl.'&'.$params;
            }

            return $this->customUrl.'?'.$params;
        }

        return $this->customUrl;
    }