WooCommerce自定义产品类型库存选项卡中缺少单独销售字段

// 添加单独销售字段
function add_individual_sale_field() {
    global $product_object;

    woocommerce_wp_checkbox( array(
        'id'            => '_individual_sale',
        'label'         => __( '单独销售', 'woocommerce' ),
        'description'   => __( '勾选此项以允许产品以独立的方式进行销售', 'woocommerce' ),
        'value'         => get_post_meta( $product_object->get_id(), '_individual_sale', true ),
    ) );
}
add_action( 'woocommerce_product_options_inventory_product_data', 'add_individual_sale_field' );

// 保存单独销售字段的值
function save_individual_sale_field( $product_id ) {
    $individual_sale = isset( $_POST['_individual_sale'] ) ? 'yes' : 'no';
    update_post_meta( $product_id, '_individual_sale', $individual_sale );
}
add_action( 'woocommerce_process_product_meta', 'save_individual_sale_field' );