code: public function run()
      {
          // NOTE: To be removed in v1.0.0. Use "ErrorHandlerIntegration" instead.
          if (static::$container->has(self::ERROR_HANDLER)) {
              $debugger = static::$container->get(self::ERROR_HANDLER);
  
              $debugger->display();
          }
  
          $request = static::$container->get(self::SERVER_REQUEST);
  
          echo (string) $this->emit($request)->getBody();
      }
docs: Emits the headers from response and runs the application.
  
  @return void