The following exception is thrown because the thumbnail might occassionally be null, so needs proper handling for it:
[error] TypeError: Drupal\file\FileUsage\DatabaseFileUsageBackend::listUsage(): Argument #1 ($file) must be of type Drupal\file\FileInterface, null given, called in /app/application/web/modules/contrib/media_thumbnails/src/Plugin/MediaThumbnailManager.php on line 140 in Drupal\file\FileUsage\DatabaseFileUsageBackend->listUsage() (line 101 of /app/application/web/core/modules/file/src/FileUsage/DatabaseFileUsageBackend.php) #0 /app/application/web/modules/contrib/media_thumbnails/src/Plugin/MediaThumbnailManager.php(140): Drupal\file\FileUsage\DatabaseFileUsageBackend->listUsage(NULL)
#1 /app/application/web/modules/contrib/media_thumbnails/media_thumbnails.module(48): Drupal\media_thumbnails\Plugin\MediaThumbnailManager->deleteThumbnail(Object(Drupal\media\Entity\Media))
#2 [internal function]: media_thumbnails_media_delete(Object(Drupal\media\Entity\Media))
Attempt to delete a media entity that does not have a thumbnail attached for whatever reason.
Return early if the media entity has no thumbnails attached.
Provide issue fork/patch.
N/A
1.0
Code
I encountered this exact problem, applied the patch by codebymikey: voilà, problem gone.
Before applying the patch, I hit error above on the typical white Drupal error page.
The code change looks fine.