Title: Fatal error in AssetsHandler.php during Customizer preview Last modified: July 5, 2026 --- # Fatal error in AssetsHandler.php during Customizer preview * Resolved [zoofy](https://wordpress.org/support/users/zoofy/) * (@zoofy) * [2 weeks, 4 days ago](https://wordpress.org/support/topic/fatal-error-in-assetshandler-php-during-customizer-preview/) * **Issue:** The plugin is throwing a fatal error that crashes the entire site ( including wp-admin) whenever WordPress’s Customizer tries to load with an invalid or expired changeset. This has happened multiple times and has taken down site access completely until resolved manually via server file access.**Error / Stack Trace: * ```wp-block-code PHP Fatal error: Uncaught Error: Call to a member function is_preview_mode() on null in /wp-content/plugins/wp-expand-tabs-free/src/Modules/ProductTabs/Frontend/AssetsHandler.php:52Stack trace:#0 wp-includes/class-wp-hook.php(341): ShapedPlugin\SmartTabsFree\Modules\ProductTabs\Frontend\AssetsHandler->enqueue_frontend_assets('')#1 wp-includes/class-wp-hook.php(365): WP_Hook->apply_filters(NULL, Array)#2 wp-includes/plugin.php(522): WP_Hook->do_action(Array)#3 wp-includes/script-loader.php(2329): do_action('wp_enqueue_scri...')#4 wp-includes/class-wp-customize-manager.php(462): wp_enqueue_scripts()#5 wp-includes/class-wp-customize-manager.php(561): WP_Customize_Manager->wp_die(0, 'Non-existent ch...')#6 wp-includes/class-wp-hook.php(341): WP_Customize_Manager->setup_theme('')#7 wp-includes/class-wp-hook.php(365): WP_Hook->apply_filters(NULL, Array)#8 wp-includes/plugin.php(522): WP_Hook->do_action(Array)#9 wp-settings.php(697): do_action('setup_theme')#10 wp-config.php(113): require_once#11 wp-load.php(50): require_once#12 wp-blog-header.php(13): require_once#13 index.php(17): require thrown in /wp-content/plugins/wp-expand-tabs-free/src/Modules/ProductTabs/Frontend/AssetsHandler.php on line 52 ``` * **How it appears to be triggered:** This occurs specifically when WordPress’s Customizer bootstrap runs with a non-existent/invalid `customize_changeset_uuid`( e.g., `WP_Customize_Manager->wp_die(0, 'Non-existent changeset...')`). It looks like `AssetsHandler->enqueue_frontend_assets()` is calling `is_preview_mode()` on an object that hasn’t been initialized in this code path, so it fatals instead of failing gracefully. * **Impact:** Since this fires during `setup_theme`, it crashes the entire site— front end and wp-admin alike — not just the Customizer preview itself. This makes it a critical severity issue for us, not just a minor edge case. * **Request:** Could you confirm whether this is a known issue, and if there’s a patch or workaround available? Happy to provide further debug info if needed. Viewing 4 replies - 1 through 4 (of 4 total) * Plugin Support [Pulak Ahmed](https://wordpress.org/support/users/pulak00/) * (@pulak00) * [2 weeks, 2 days ago](https://wordpress.org/support/topic/fatal-error-in-assetshandler-php-during-customizer-preview/#post-18956967) * Hello [@zoofy](https://wordpress.org/support/users/zoofy/), * Thanks for contacting us and sharing the error details. * We have not yet received a similar report. At this time, the issue appears to be site-specific, or it may be reproducible in a comparable setup to the one you currently have. We have therefore shared the available details with our development team for further investigation. * We remain committed to identifying the root cause of the issue and determining the appropriate fix. Once we have resolved it, we will release an updated version of the plugin as soon as it is ready. * Your understanding and cooperation would be much appreciated. * Kind regards, Pulak Ahmed,Support Engineer | ShapedPlugin * Plugin Support [Pulak Ahmed](https://wordpress.org/support/users/pulak00/) * (@pulak00) * [1 week, 5 days ago](https://wordpress.org/support/topic/fatal-error-in-assetshandler-php-during-customizer-preview/#post-18961624) * Hello [@zoofy](https://wordpress.org/support/users/zoofy/), * We have released a new version(**3.1.6**) of the plugin addressing the issue. We request you update the plugin and let us know if the issue persists. * We look forward to your reply. * Kind regards, Pulak Ahmed,Support Engineer | ShapedPlugin * Thread Starter [zoofy](https://wordpress.org/support/users/zoofy/) * (@zoofy) * [1 week, 3 days ago](https://wordpress.org/support/topic/fatal-error-in-assetshandler-php-during-customizer-preview/#post-18963188) * [@pulak00](https://wordpress.org/support/users/pulak00/) Thanks. I have updated and will continue to monitor my site and let you know if it pops up again. So far no errors yet! * Plugin Support [Pulak Ahmed](https://wordpress.org/support/users/pulak00/) * (@pulak00) * [1 week, 2 days ago](https://wordpress.org/support/topic/fatal-error-in-assetshandler-php-during-customizer-preview/#post-18963220) * Hi [@zoofy](https://wordpress.org/support/users/zoofy/), * Feel free to contact us if you need further assistance. * Have a nice day! Viewing 4 replies - 1 through 4 (of 4 total) You must be [logged in](https://login.wordpress.org/?redirect_to=https%3A%2F%2Fwordpress.org%2Fsupport%2Ftopic%2Ffatal-error-in-assetshandler-php-during-customizer-preview%2F%3Foutput_format%3Dmd&locale=en_US) to reply to this topic. * ![](https://ps.w.org/wp-expand-tabs-free/assets/icon-256x256.gif?rev=3502431) * [Custom Product Tabs for WooCommerce & WordPress Tabs Builder – Smart Tabs](https://wordpress.org/plugins/wp-expand-tabs-free/) * [Frequently Asked Questions](https://wordpress.org/plugins/wp-expand-tabs-free/#faq) * [Support Threads](https://wordpress.org/support/plugin/wp-expand-tabs-free/) * [Active Topics](https://wordpress.org/support/plugin/wp-expand-tabs-free/active/) * [Unresolved Topics](https://wordpress.org/support/plugin/wp-expand-tabs-free/unresolved/) * [Reviews](https://wordpress.org/support/plugin/wp-expand-tabs-free/reviews/) * 4 replies * 2 participants * Last reply from: [Pulak Ahmed](https://wordpress.org/support/users/pulak00/) * Last activity: [1 week, 2 days ago](https://wordpress.org/support/topic/fatal-error-in-assetshandler-php-during-customizer-preview/#post-18963220) * Status: resolved