Dry firing a little should not damage the weapon, as the change in pressure is not significant enough (but exists). However, you should not dry fire A LOT, just like you would not fire the gun loaded A LOT at once.
Dry firing all the time may shorten the life of the rifle, but doing it a little is not harmful, in a way that firing with or without a bb uses the component, so it's not the dry firing itself that will kill your gun.
I hope I'm clear (and not mistaken).
K3vX | Airsoft Gunsmith/Gun doctor in training.
Feel free to contact me in your preferred language and I'll gladly answer.