Fatal error: Uncaught Error: Call to undefined function wp_is_block_theme() in /home/5/l/lillesandsv/www/wp-content/plugins/ultimate-addons-for-gutenberg/classes/class-uagb-front-assets.php:137 Stack trace: #0 /home/5/l/lillesandsv/www/wp-includes/class-wp-hook.php(292): UAGB_Front_Assets->enqueue_asset_files('') #1 /home/5/l/lillesandsv/www/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters(NULL, Array) #2 /home/5/l/lillesandsv/www/wp-includes/plugin.php(484): WP_Hook->do_action(Array) #3 /home/5/l/lillesandsv/www/wp-includes/script-loader.php(2027): do_action('wp_enqueue_scri...') #4 /home/5/l/lillesandsv/www/wp-includes/class-wp-hook.php(292): wp_enqueue_scripts('') #5 /home/5/l/lillesandsv/www/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters(NULL, Array) #6 /home/5/l/lillesandsv/www/wp-includes/plugin.php(484): WP_Hook->do_action(Array) #7 /home/5/l/lillesandsv/www/wp-includes/general-template.php(3009): do_action('wp_head') #8 /home/5/l/lillesandsv/www/wp-content/themes/twentytwentyone/header.php(20): wp_head() #9 /home/5/l/lillesandsv/www/wp-includes/template.php(730): require_once('/home/5/l/lille...') #10 /home/5/l/lillesandsv/www/wp-includes/template.php(676): load_template('/home/5/l/lille...', true, Array) #11 /home/5/l/lillesandsv/www/wp-includes/general-template.php(48): locate_template(Array, true, true, Array) #12 /home/5/l/lillesandsv/www/wp-content/themes/twentytwentyone/page.php(12): get_header() #13 /home/5/l/lillesandsv/www/wp-includes/template-loader.php(106): include('/home/5/l/lille...') #14 /home/5/l/lillesandsv/www/wp-blog-header.php(19): require_once('/home/5/l/lille...') #15 /home/5/l/lillesandsv/www/index.php(17): require('/home/5/l/lille...') #16 {main} thrown in /home/5/l/lillesandsv/www/wp-content/plugins/ultimate-addons-for-gutenberg/classes/class-uagb-front-assets.php on line 137