code: protected function handleFallbackExceptionMessage($exception, $previousException)
      {
          $msg = "An Error occurred while handling another error:\n";
          $msg .= (string) $exception;
          $msg .= "\nPrevious exception:\n";
          $msg .= (string) $previousException;
          if (YII_DEBUG) {
              if (PHP_SAPI === 'cli') {
                  echo $msg . "\n";
              } else {
                  echo '<pre>' . htmlspecialchars($msg, ENT_QUOTES, Yii::$app->charset) . '</pre>';
              }
          } else {
              echo 'An internal server error occurred.';
          }
          $msg .= "\n\$_SERVER = " . VarDumper::export($_SERVER);
          error_log($msg);
          if (defined('HHVM_VERSION')) {
              flush();
          }
          exit(1);
      }
docs: Handles exception thrown during exception processing in [[handleException()]].
  @param \Exception|\Throwable $exception Exception that was thrown during main exception processing.
  @param \Exception $previousException Main exception processed in [[handleException()]].
  @since 2.0.11