I did Google on "手不空回 - Never come back empty-handed when you punch" and I find at least 4 TCMA systems has this. It's a quite common principle after all.
In wing chun the kuit as I learned it was when hand goes out it does not return and this refers to using the extended hand to attempt to further disrupt your opponent by pressing or pulling or jerking him and the tactic is not limited to his arms or his blocks.