Various forgotten fixups necessary for emails being nullable

[myieye]

Fixes #657

FYI the form validation change (.nullable()) doesn't allow a user to delete an existing email address.
But even if they could the server would ignore it, because it ignores empty values.

[github-actions]

UI unit Tests

11 tests  ±0   11 ✅ ±0   0s ⏱️ ±0s
 3 suites ±0    0 💤 ±0 
 1 files   ±0    0 ❌ ±0 

Results for commit 8aba105. ± Comparison against base commit 85f4c8b.

♻️ This comment has been updated with latest results.

[github-actions]

C# Unit Tests

26 tests   26 ✅  4s ⏱️
 6 suites   0 💤
 1 files     0 ❌

Results for commit 8aba105.

♻️ This comment has been updated with latest results.

[hahn-kev]

looks reasonable to me, I didn't test it though

[rmunn]

Tested, and everything seems to work. One feature that's not in here is editing the username of a user with no email (can edit display name, but not username). That should probably be in a different PR, though. This one LGTM.

[rmunn]

One issue revealed in testing: if you edit a user with no email, type something into the email box, then delete it, you can't submit the form. (Because the field went from undefined/null to '' (empty string) and now zod won't allow form submission).

I triggered this by accident when I was trying to edit the display name of a bulk-added user, and edited the email field by mistake.

[rmunn]

Just turned up an issue I missed in earlier testing: if you accidentally type into the email field, then delete what you typed, you end up unable to submit the form.

Allowing that scenario would involve treating an empty string in the email column as if it was a null/undefined. If we add that, we'll also accidentally enable admins to delete a user's email address. That may or may not be desirable. Still, I think this scenario should be fixed somehow.

[myieye]

I think usernames can be read-only. I think that's fairly common.
Email addresses can't, because a user might (e.g.) want to migrate to a different provider.

[myieye]

@rmunn I mapped falsy emails to null if the user doesn't currently have an email address (8aba105)

[rmunn]

Great; everything looks good now.