To see 0 users would be a bit awkward.You'd need to log on to see if anyone were on line and that would mean 1 user. The only time there are 0 users is when nobody is logged on. And this takes us into the realms of such questions as:
In the total absence of light, is a black cat still black?
When you're the last one to leave a room, once you close the door is it still there?
If a tree crashes to the ground in the middle of a forest and there's nobody around, does it still make a noise?
Why do we never see baby pigeons?
Why do people who repair shoes also cut keys?
All of which gives me a right headache!!