Holes can be very useful but also dangerous if used unwisely. Never stack your holes.
Nothing is more manageable but also has some inherent dangers. I once left some nothing laying on top of something and ended up with nothing. Nothing can be stacked with nothing or something but nothing always needs to be placed under something rather than vice versa.
Most people tend to put something where they have been storing nothing, but they are sensible enough to put nothing on top of things that are really fragile and delicate.