The SafeString change at /r/14299 introduced some regressions with

rendering changes to comma-separated fields. After deploying, we were

getting a bunch of IndexError crashes trying to render when the added

or removed list was empty. My initial fix for this was to use

walrus-operators to check the truthiness of those values before doing

anything else.
This exposed another issue with the change, which was that the inner

[values] caused entries to be double-wrapped, which ended up making it

so we'd show only the first item in the added or changed list, but then

rendering it as a python list repr instead. For example, a change that

added bugs 123 and 456 would show "Bugs: + ['123']". Really what needs

to happen is going back to the previous implementation with separate

branches for the single-line and multi-line modes.

Added a test class for the BugsField. Verified that these tests failed

  before the change, and succeeded afterward.
Verified that added and removed items in BaseCommaSeparatedField

  subclasses rendered correctly, including both the one-per-line and the

  combined mode (specifically tested bugs, users, and file attachments).