code: public function onError(Request $request = null)
  	{
  		$request = $request ?: Request::current();
  		$res = $this->error()($request);
  		if ($res && !$res->ignoreDefaultHeaders) $res->header($this->defaultHeaders);
  		return $res;
  	}
docs: Error response
  
  @param Request|null $request incoming request
  
  @return Response