AngularUI: Normalize empty options for select inputs #15120
Description
Resolves #15108
Related #15077, #15083
TODO: Set empty option as "Not Assigned" for Create & Update screens
Checklist
- I fully tested it as developer / designer and created unit / integration tests
- I've assigned reviewer, related labels and set a milestone for this PR
How to test it?
- We can use Lepton for test