Cannot upload file of type image I am experiencing a really strange behavior I have never seen before with Drupal. I am able to upload files of every type but not images. The files system is public. The problem appears on the local test server and on the live server.
Error message:
The image upload widget shows the standard error box logging:
**The file xyz.jpg could not be uploaded.

This value should not be null**

This issue appears on the whole site on every image of the file field widget within the backend.
Even the file upload for Drupal's &quot;File Archive&quot; does just work with every other file type than 'jpg', 'jpeg', 'gif', 'png' file types.
The issue appeared after updating to the &quot;web/&quot; file structure while also updating the core to 8.8. I tried to update to 8.9.12 including every module installed but the error when trying to upload a file stays.
I rechecked all the settings regarding &quot;tmp folder&quot; and also tested the folder access rights (chown, chmod). It is set to 777.
I updated the database (drush updb) and also rebuild the cache (drush cr).
No PHP error log is created (not in Drupals Watchdog or the apache log).
I am sure that it is not a configuration issue as I am able to upload files that are not image files without problems. Another interesting bit is that when uploading a file it is actually created in the final sites/default/files location. The file also has the correct owner and access rights.
I could not find a related issue when researching nor I am able to come up with another idea. I even tried to change the file system to private, created new entities with image or file fields and tried different image upload widgets - nothing seems to work.
Any help is greatly appreciated.
After spending good 20hours with investigating the issue I was able to fix it by repairing an entity error in the database via un and installing the file_entity module.