Fatal error: Uncaught Error: Class 'WP_Upgrader_Skin' not found in /var/www/html/nakatsus/katey/wp-admin/includes/class-plugin-installer-skin.php:18 Stack trace: #0 {main} thrown in /var/www/html/nakatsus/katey/wp-admin/includes/class-plugin-installer-skin.php on line 18