check for "product_id" array key before switch statement in commerce_registration_form_alter()

Hello again,

I am getting the following error message on a product display page with a cart that has no commerce products marked as active:

Notice: Undefined index: product_id in commerce_registration_form_alter() (line 298 of /Users/choicelildice/websites/tentiko/site/sites/all/modules/contrib/commerce_registration/commerce_registration.module).

A simple check for the key before the switch statement starting on line 298 would do the trick:
if (array_key_exists('product_id', $form)){}

Thanks again