Fatal error if thumbnail image does not exist

Additionally, I have added the use of the generic thumbnail as fallback and added a message to the logs.

I think that the changes in the latest MR can be improved. I mean, the following is not a very usual situation, but I will try to describe a particular case that we spotted: imagine you are working on different environments, it can happen that if you want to "clone" one of them importing the database and then the configuration with changes you did locally, you will have the pdf entities but not the physical files on your filesystem. In this case you will receive PHP warnings because the files and the derivative images don't exist locally.

Would it be better to add also a second condition to check in the handleDerivative method of the ImageFieldFormatterElementViewTrait?

    if (empty($file) || !file_exists(\Drupal::service('file_system')->realpath($file->getFileUri()))) {
      $this->mediaPdfThumbnailImageManager->getLogger()->warning('No file found for image id: @imageId. Using generic thumbnail instead', ['@imageId' => $imageId]);
      $file = $this->mediaPdfThumbnailImageManager->getGenericThumbnail(TRUE);
    }

Thanks for your feedback. The new changes should add a proper way to check for the existence of files with both local and remote storage system.