[issue_tracker] null option assignee

[regisoc]

Brief summary of changes

This PR:

• Forces an internal server error JSON response on db update error, which allows to actually see front-end swal error.
• Bug fixes the "null" userID assignee that was the current user (i.e. added based on a composed string "full name (userid)").

Testing instructions (if applicable)

1. Go to Report > issue tracker
2. click on "new issue".
3. assert no "null" user is in the "assignee" dropdown
4. create new issue with some basic fileds.
5. click inside the previously created issue inside the main issue tracker table.
6. click on "assignee" dropdown.
7. assert no "null" user is in the "assignee" dropdown.

Link(s) to related issue(s)

• Resolves [issue_tracker] Null option in user assignees #9128

[driusan]

Tested it on my sandbox, looks like the null isn't there anymore.