be a moot question

To be a topic that can no longer be questioned or debated. Whether or not he's the best person for the job is a moot question now that he's tenured. A: "Have you looked at Harvard's program?" B: "That's a bit of a moot question, don't you think? I've already accepted a place at NYU." A: "I'm sorry, I didn't know you were interested in the antique record player." B: "Well, it's a moot question now that you've sold it, huh?"

be a moot ˈpoint/ˈquestion

be a subject that people disagree on or are uncertain about: It’s a moot point whether women or men make better drivers.A moot was a group of people who met to discuss questions of local or national law during the Anglo-Saxon period. A moot point was a question of law discussed at this meeting.