Error on PHP 8

Fatal error: Uncaught TypeError: array_merge(): Argument #1 must be of type array, null given in /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/plugins/checkout-field-editor-and-manager-for-woocommerce/includes/class-awcfe-fields.php:288 Stack trace: #0 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/plugins/checkout-field-editor-and-manager-for-woocommerce/includes/class-awcfe-fields.php(288): array_merge(NULL, Array) #1 [internal function]: AWCFE_Fields->{closure}(Array) #2 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/plugins/checkout-field-editor-and-manager-for-woocommerce/includes/class-awcfe-fields.php(331): array_map(Object(Closure), Array) #3 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/plugins/checkout-field-editor-and-manager-for-woocommerce/includes/class-awcfe-front-end.php(426): AWCFE_Fields->getFields(Array) #4 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-includes/class-wp-hook.php(292): AWCFE_Front_End->get_checkout_fields(Array) #5 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-includes/plugin.php(212): WP_Hook->apply_filters(Array, Array) #6 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/plugins/woocommerce/includes/class-wc-checkout.php(265): apply_filters('woocommerce_che...', Array) #7 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/plugins/woocommerce/templates/checkout/form-checkout.php(34): WC_Checkout->get_checkout_fields() #8 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/plugins/woocommerce/includes/wc-core-functions.php(345): include('/home/virtual/v...') #9 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/plugins/woocommerce/includes/shortcodes/class-wc-shortcode-checkout.php(293): wc_get_template('checkout/form-c...', Array) #10 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/plugins/woocommerce/includes/shortcodes/class-wc-shortcode-checkout.php(67): WC_Shortcode_Checkout::checkout() #11 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/plugins/woocommerce/includes/class-wc-shortcodes.php(72): WC_Shortcode_Checkout::output('') #12 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/plugins/woocommerce/includes/class-wc-shortcodes.php(95): WC_Shortcodes::shortcode_wrapper(Array, '') #13 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-includes/shortcodes.php(343): WC_Shortcodes::checkout('', '', 'woocommerce_che...') #14 [internal function]: do_shortcode_tag(Array) #15 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-includes/shortcodes.php(218): preg_replace_callback('/\\[(\\[?)(woocom...', 'do_shortcode_ta...', '[woocommerce_ch...') #16 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-includes/class-wp-hook.php(292): do_shortcode('[woocommerce_ch...') #17 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-includes/plugin.php(212): WP_Hook->apply_filters('[woocommerce_ch...', Array) #18 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-includes/post-template.php(253): apply_filters('the_content', '<p>[woocommerce...') #19 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/themes/twentytwentyone/template-parts/content/content-page.php(29): the_content() #20 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-includes/template.php(732): require('/home/virtual/v...') #21 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-includes/template.php(676): load_template('/home/virtual/v...', false, Array) #22 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-includes/general-template.php(204): locate_template(Array, true, false, Array) #23 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/themes/twentytwentyone/page.php(17): get_template_part('template-parts/...') #24 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-includes/template-loader.php(106): include('/home/virtual/v...') #25 /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-blog-header.php(19): require_once('/home/virtual/v...') #26 /home/virtual/vps-298d74/3/3270ea6364/public_html/index.php(17): require('/home/virtual/v...') #27 {main} thrown in /home/virtual/vps-298d74/3/3270ea6364/public_html/wp-content/plugins/checkout-field-editor-and-manager-for-woocommerce/includes/class-awcfe-fields.php on line 288

I have tried using the default WP theme — the same error is thrown.

Any tips would be great — it’s stable on PHP 7.4 …