如何在wordpress中检查该短代码是否为空

I am using the WooCommerce plugin. I created a sale page and use [sale_products] shortcode of WooCommerce. It shows me all sales product perfectly, now I want that if there are no sale products, the message will be show "there is no sale product".

Like this:

if(!empty([sale_products])) {
    [sale_products]
} else {
    // message
}

Is there any way to handle this?

$output = do_shortcode('[sale_products]');
    if($output !== '') {
    [sale_products]
}