Then there is a method which I've encountered less commonly. The attacker puts something in, but gets nothing back. There is neither push nor pull. A process is definitely happening, something significant is transpiring with the data input. But there is nothing really in the way of output. The attack may redirect, or not. The attacker may be unbalanced, or not. Whatever happens is not "done" in the regular sense of doing.
Such methods or functions can be said to be "void."
If there is a punch to your face you can redirect it or not. You can unbalance the attacker or not.
If you redirect/unbalance - you do something and there is no "void" in the sense you suggested where the input - punch, causes an output - redirection/unbalancing.
If you didn't, you simply get a bloody nose.