Fatal error: Uncaught Error: Class "WP_Widget" not found in /var/www/esc.fs.cvut.cz/_HOSTING_WEB2_/wp-includes/widgets/class-wp-widget-calendar.php:17 Stack trace: #0 {main} thrown in /var/www/esc.fs.cvut.cz/_HOSTING_WEB2_/wp-includes/widgets/class-wp-widget-calendar.php on line 17