I used to play a game as a kid where I'd close my eyes and try not to see or imagine anything. To keep a black empty universe as the only thing I see, for as long as possible. It isn't easy!
I always found it odd you'd want to deprive yourself from excercising mind this way by medidating = practicing not thinking.
I believe it helped me a lot when programming and thinking about problems in general.
Rest is part of exercise