[FIX] Look & Feel theme preference gave a PHP Warning: Undefined array key "theme" in \lib\prefs\site.php on line 11 and 12
Ticket: https://avan.tech/item111337
Each time you modify the theme site (theme preference), you'll see these two errors:
Warning: Undefined array key "theme" in \lib\prefs\site.php on line 11
Warning: Undefined array key "theme" in \lib\prefs\site.php on line 12