code: protected function renderException($exception)
      {
          if (Yii::$app->has('response')) {
              $response = Yii::$app->getResponse();
              // reset parameters of response to avoid interference with partially created response data
              // in case the error occurred while sending the response.
              $response->isSent = false;
              $response->stream = null;
              $response->data = null;
              $response->content = null;
          } else {
              $response = new Response();
          }
  
          $response->setStatusCodeByException($exception);
  
          $useErrorView = $response->format === Response::FORMAT_HTML && (!YII_DEBUG || $exception instanceof UserException);
  
          if ($useErrorView && $this->errorAction !== null) {
              $result = Yii::$app->runAction($this->errorAction);
              if ($result instanceof Response) {
                  $response = $result;
              } else {
                  $response->data = $result;
              }
          } elseif ($response->format === Response::FORMAT_HTML) {
              if ($this->shouldRenderSimpleHtml()) {
                  // AJAX request
                  $response->data = '<pre>' . $this->htmlEncode(static::convertExceptionToString($exception)) . '</pre>';
              } else {
                  // if there is an error during error rendering it's useful to
                  // display PHP error in debug mode instead of a blank screen
                  if (YII_DEBUG) {
                      ini_set('display_errors', 1);
                  }
                  $file = $useErrorView ? $this->errorView : $this->exceptionView;
                  $response->data = $this->renderFile($file, [
                      'exception' => $exception,
                  ]);
              }
          } elseif ($response->format === Response::FORMAT_RAW) {
              $response->data = static::convertExceptionToString($exception);
          } else {
              $response->data = $this->convertExceptionToArray($exception);
          }
  
          $response->send();
      }
docs: Renders the exception.
  @param \Exception|\Error $exception the exception to be rendered.