strtolower() expects parameter 1 to be string, array given in /var/www/apache2php53/ezp/vendor/tedivm/stash/src/Stash/Item.php on line 525

steps to reproduce:
1 - log in "admin2" with admin
2 - active debug output
3 - click on "Media Library" link
4 - click on "Images" link
5 - click on "Create New"
6 - click on "Images"
7 - fill form with any text
8 - upload any image
9 - click on "Send for publish"
10- Verify on debug redirect the warning