I'm configuring my project workflow and have figured out how to clear out the Assignee value when an issue is moved back to Backlog by adding a post function to the "Backlog" transition (Update Issue Field - Issue Field: Assignee; Field Value: Unassigned). However, I don't see how to do the same for the "Fix Version/s" value (it's not in the Issue Field drop-down).
What do I need to do to have the Fix Version/s value removed when an issue is moved back to the Backlog?