Fatal error: Uncaught Error: Call to a member function flush_rules() on null in /var/www/html/wp-includes/rewrite.php:273 Stack trace: #0 /var/www/html/wp-content/plugins/glossary-by-codeat/includes/CPT_Core/CPT_Core.php(335): flush_rewrite_rules() #1 /var/www/html/wp-includes/class-wp-hook.php(286): CPT_Core->flush_permalink('gutenberg/guten...', false) #2 /var/www/html/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters('', Array) #3 /var/www/html/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #4 /var/www/html/wp-admin/includes/plugin.php(713): do_action('deactivated_plu...', 'gutenberg/guten...', false) #5 /var/www/html/wp-content/plugins/gutenberg/gutenberg.php(16): deactivate_plugins(Array) #6 /var/www/html/wp-settings.php(305): include_once('/var/www/html/w...') #7 /var/www/html/wp-config.php(114): require_once('/var/www/html/w...') #8 /var/www/html/wp-load.php(37): require_once('/var/www/html/w...') #9 /var/www/html/wp-blog-header.php(13): require_once('/var/www/html/w...') #10 /var/www/html/index.ph in /var/www/html/wp-includes/rewrite.php on line 273