Steps to reproduce
Go to Admin Panel - Content Types - Users - User - Edit
Select signature checkbox
Click "remove selected field definitions"
FatalErrorException in vendor/ezsystems/platform-ui-bundle/Controller/ExceptionController.php line 25:
Error: __clone method called on non-object
Issue originally reported in https://jira.ez.no/browse/EZP-26397 and fixed in https://jira.ez.no/browse/EZP-26397
Database content of the ezstudio-demo should to be updated to be relevant with the latest changes.