Fatal error: Uncaught Error: Class "WP_Upgrader" not found in /var/www/vhosts/awxpokmt.host213.checkdomain.de/htdocs/playground/wordpress/wp-admin/includes/class-theme-upgrader.php:21 Stack trace: #0 {main} thrown in /var/www/vhosts/awxpokmt.host213.checkdomain.de/htdocs/playground/wordpress/wp-admin/includes/class-theme-upgrader.php on line 21