Parent widget can fail loudly during work item creation

In some cases when pasting a link to a parent and selecting that item during work item creation, the selection of a parent causes the sidebar to disappear completely.

Example:

1. New issue from https://gitlab.com/gitlab-org/gitlab/-/issues/new
2. Click Edit next to Parent in right sidebar
3. Paste in an epic URL (e.g. &10893)
4. Select list is correctly filtered to that epic
5. Click the epic in the list (UX Improvements)