Webhook processing fails when list id does not match any list configured in Magento

[Santiagoebizmarts]

Preconditions

mc-magento2 1.0.29

Steps to reproduce

1. Set up the extension making sure to select one list.
2. Create Webhook.
3. Add in that MailChimp list without doing nothing in Magento.
4. Change the configured list for the extension.

Expected result:

Subscriber not added to Magento and no errors thrown.

Actual result:

Error message thrown: Call to a member function count() on null in /chroot/home/diamond6/diamonddesignsuniforms.com/html/app/code/Ebizmarts/MailChimp/Cron/Webhook.php:191

Additional information

When trying to fetch the customer or subscriber for the store where the list is configured, it returns null because that list is not configured for any Magento scope.
count function can not be used in null.