When using the Test Runs List Gadget, if the Assignee of the run has been deleted or removed, it's not possible to generate it

Description
When using the Test Runs List Gadget, if the Assignee of the run has been deleted or removed, it's not possible to generate the list on the gadget.

How to reproduce

1. You need to have a User who has been deleted or removed as an Assignee of a Test Run
2. Add the Test Run List Gadget and select it on the Test Run Assignee field

Actual result/Attachments
The Gadget is not loaded and shows the "Unexpected error occurred."

Expected result
It should show the Test Runs even if the Assignee has already been removed or deleted.

Workaround
The workaround possible for now is to update the assignees on the runs.