Fatal error "Stream must be a resource"

This is the commit that introduced the error: https://git.drupalcode.org/project/rokka/-/commit/5387a5ff229eb96f5aff8d...

It looks like this code went missing which is responsible for injecting the RokkaToolkit into the ImageFactory.

  /**
   * {@inheritdoc}
   */
  public function get($source = NULL, $toolkit_id = NULL) {
    return new Image($this->toolkitManager->createInstance('rokka'), $source);
  }

I think the problem in my affected project was that the GD toolkit is set up as the default. This should have been set to Rokka instead, but since in previous versions the Rokka toolkit was forced as the default by overriding the ImageFactory it was now unexpectedly switching back to GD when processing images intended for Rokka.

Maybe we can provide an update hook to set the default toolkit to Rokka for users who are upgrading from an older version? I am not sure if we should set it as the default on new installations though. The user should be free to use GD / ImageMagick / Rokka for different images depending on their use case.

With the patch and switching the default toolkit to Rokka the fatal error is gone in my project. Setting to Needs Review.