Cornyn mentioned it in his opening statement yesterday:

That is one reason why the American Bar Association has long said that judges cannot ethically make any pledges with regard to cases or issues that are likely to come before them. It is also why every single Supreme Court Justice in the past has declined to answer questions during their confirmation hearings
whenever they felt their impartiality and independence might be threatened. As Justice Ginsburg—one of the last Supreme Court Justices confirmed by the Senate—noted not too long ago, “in accord with a longstanding norm, every Member of [the current Supreme] Court declined to furnish such information to the Senate . . . . [T]he line each [Justice] drew in response to pre-confirmation questioning . . . is crucial to the health of the Federal Judiciary.”
I know that some members of this Committee, through their questions, will try to entice you not to follow the rules of ethics and the long tradition described by Justice Ginsburg. But that should not concern you, Judge Roberts. Don’t take the bait. Do exactly the same thing every nominee—Republican and Democrat alike—has done. Decline to answer any question that you feel would compromise your ability to do your job. The vast majority of the Senate, I am convinced, will not punish you for doing so. Rather, I am convinced that the vast majority of the Senate will respect you for this decision because it will show you to be a person of great integrity and independence, unwilling to trade your ethics for a confirmation vote.