protected function getErrorPageFile($statusCode)
    {
        $errorpage = null;
        if(isset($this->error_pages[$statusCode])) {
            $errorpage = $this->error_pages[$statusCode];
        }else if(isset($this->error_pages[substr($statusCode,0,2).'x'] )) {
            $errorpage = $this->error_pages[substr($statusCode,0,2).'x'];
        }
        
        if(!$errorpage || !is_file($errorpage)) return null;
        
        return $errorpage;
    }