TOPIC: When deleting order from cart, receive invalid argument erro

When a customer deletes an order from the cart, before checking out, we get the following error message:

Warning: Invalid argument supplied for foreach() in /<site home>/components/com_dtregister/controllers/event.php on line 528

However, it actually does delete the order from the cart successfully. It's just an annoying error.

Here is what line 528 says:

528: foreach(DT_Session::get('Setting.User') as $key => $user) {
528: DT_Session::set('Setting.User.'.$key.".Index" ,$key);

Using the latest of both DTRegister and Joomla.
1.5.26 &2.7.21 respectively.