Show possible missing values in listbox toggle text

Even if we would input a missing value in a listbox, listbox could show it as the current value. This would make our component work even non-happy cases.

Description

The following discussion from gitlab!188178 (merged) should be addressed:

• @cwoolley-gitlab started a discussion: (+1 comment)

  questions (non-blocking):

  • Is there any way the user could possibly break things or make the page blow up by manually editing the URL params to enter some invalid values? If so, do we care?
  • And is there any way this user input could make it to the backend and cause any problems or security concerns there? I think not, but just mentioning it.