code: private function set404()
      {
          $this->response->setStatusCode(404);
          $content = '404 Not Found';
          if (file_exists($this->packageRoot . '/view/404.html.php')) {
              $content = (new Native($this->packageRoot))->getContent('404.html.php');
          }
          $this->response->setContent($content);
      }
docs: Set 404 code and content.