Is empty tank bad for Respironics cpap?

This morning when I awoke, I discovered that all the water in the tank was used up. Since I had checked the amount of water in the tank before I set it to be "on" -- before going to sleep-- it's clear that I used more water than usual.

My question is: how does that impact the machine? does the humidifier have an "auto off" mechanism when it's empty? Is the plate staying hot nonetheless? And is this detrimental to the longevity of the machine?