Fatal error: Uncaught Error: Class "WP_Upgrader" not found in /usr/home/FixAGD/domains/dabrowagornicza.org.pl/public_html/wp-admin/includes/class-core-upgrader.php:25
Stack trace:
#0 {main}
  thrown in /usr/home/FixAGD/domains/dabrowagornicza.org.pl/public_html/wp-admin/includes/class-core-upgrader.php on line 25