Validation of Custom Product Metadata

I have created some custom fields to store some custom meta data for a woocommerce product. This all works fine but how can I raise an error if a value is provided for example? There are many examples on how to store meta data but haven’t been able to find any examples concerning validation of that data.

       add_action('woocommerce_process_product_meta', function($post_id) {
            if(isset($_POST['some_custom_meta']) {
                //save to database
            } else {
                //raise an error? How?
        });