crashes when combined with Markdown filter

The problem is in Markdown:

  public function process($text, $langcode = NULL) {
    // Only use the parser to process the text if it's not empty.
    if (!empty($text)) {
      $language = $langcode ? \Drupal::languageManager()->getLanguage($langcode) : NULL;
      $text = $this->getParser()->parse($text, $language);
    }
    return new FilterProcessResult($text);
  }

The parameter to FilterProcessResult is supposed to be a string.

Hi @joachim,

Is this issue occurs in 3.0.x?

I've not tried the dev release, but I can see from the MR the problem exists there too.

MR LGTM.

I was able to reproduce the error this way:

1. On a text format, set the Pathologic filter after the Markdown filter
2. Try to render a text using the configured text format.

I added an unit test (oof) and I merged the changes!