Warning: count(): Parameter must be an array or an object that implements Counta

hi, I ask you for help your plugin is fantastic, but with php 7.2 or higher I find this error, can you correct it?

Waitlist For WooCommerce pro 1.5

Warning: count(): Parameter must be an array or an object that implements Countable in /wp-content/plugins/waitlist-woocommerce-premium/admin/templates/xoo-wl-waitlist-table.php on line 50

***line 50***
$total_users = count(json_decode(get_post_meta($product_id,’_xoo-wl-users’,true),true));
if($total_users === 0) continue;