Failing to select a Usage when creating a DeDUPE rule throws an error. It should be trapped and an error message created

I tested this on drupal.demo.civirm.org today

Steps to replicate the issue:
Go to Contacts > Find and Merge Duplicate Contacts
Select Add Rule for individuals
DO NOT select a Usage value. On drupal.demo.civicrm.org they were not selected by default
Select one or more fields. Set the weight and threshold.
save.
Error Thrown.