Default tester can't be assigned via TP

[atodorov]

Component (web, API, etc)

web

Version or commit hash (if applicable)

DEMO

How often reproducible

Always

Steps to Reproduce

1. Create a Test Plan
2. Add some Test Cases to it.
3. Click the Cases tab
4. Select Test Cases
5. Click the Default Tester button
6. Enter a valid tester email and click Update

Actual results

Nothing happens in UI, the POST ajax request fails with a 500 ISE.

Expected results

Default tester is updated.

Additional info

[atodorov]

Note: appears to be happening either when an invalid username/email is entered -> raises ObjectNotFound exception which causes the view to fail

NOTE2: the UI widget claims both username and email are supported as inputs but the code only searches via username.