Fatal error when field is set as required and empty

Hello,

using the free version here.
When the product custom field is set to required and the customer does not fill it in, wp generates a fatal error

Fatal error: Uncaught Exception: <strong>N°abonné</strong> is required field. in /xxx/wp-content/plugins/flexible-product-fields/classes/fpf-cart.php:174 Stack trace: #0 /xxx/wp-content/plugins/flexible-product-fields/classes/fpf-cart.php(285): FPF_Cart->get_field_data(Array, Array, '', 2960, '') #1 /xxx/wp-includes/class-wp-hook.php(294): FPF_Cart->woocommerce_add_cart_item_data(Array, 2960, '') #2 /xxx/wp-includes/plugin.php(212): WP_Hook->apply_filters(Array, Array) #3 /xxx/wp-content/plugins/woocommerce-subscriptions/includes/class-wc-subscriptions-cart-validator.php(44): apply_filters('woocommerce_add...', Array, 2960, '', 1) #4 /home/cbbccqn/www/wp-includes/class-wp-hook.php(292): WC_Subscriptions_Cart_Validator::maybe_empty_cart(true, 2960, 1) #5 /xxx/wp-includes/plugin.php(212): WP_Hook->apply_filters(true, Array) #6 /xxx/wp-content/plugins/woocommerce/includes/class-wc-form-handler.php(820): apply_f in /xxx/wp-content/plugins/flexible-product-fields/classes/fpf-cart.php on line 174

Thanks for any feedback;
Bye;