Issues remain associated to deleted request types

Issue Summary

If a request type that's currently in use is deleted, the issues remain associated to them on background.
e.g.: The JQL "request type is empty" won't return those issues because the association with the deleted request type still exist.

Steps to Reproduce

1. Create a JSD request
2. Delete the associated request type
3. Search for "request type is empty" and the issue won't be returned.

Expected Results

The association between issues and the deleted request types is removed.

Actual Results

The issues remain associated to non existing request types.

Customers are able to view the issue via the portal, but the details are not available. 

Customers can also type a comment, but it will show an error if they try to save it.

Workaround

N/A