Question: I had my first session as Dungeon Master (DM) yesterday playing pathfinder ("First Steps In Lore" from the "Pathfinder Society" series) with a group of first-time tabletop RPG players (myself included). Overall the sessions went well, a good crash course for everyone and everyone seemed to enjoy themselves.

My question is a problem I personally had while DMing. I taught the players that they can roll for perception to check things out, finding traps and secrets, etc. The players got the idea and started saying "roll for perspection to check out the room", etc., and they found a couple of traps that way, and that's fine. The problem I had was: What do I do with all the "useless" rolls?

Most of the time they were rolling when there was nothing to find. Even on a natural 20 I kind of just described the room in more detail while saying something like "but there is nothing of interest".

Is there a better way of approaching this? Do I make something up?

I'd like to add: I would prefer my players roll their perception checks when they are actively looking. I am not a fan of the hidden-DM-rolls-for-all-perception idea.

Answer: 
have the players roll a bunch of perception rolls at the beginning, list them all and cross them off as you go, they know the rolled them, but have no idea if they see nothing because of a bad roll, or if there is truely nothing to see.
If they fail, make them perceive something wrong. A misperception can happen anytime, specially if they're really looking for something. Characters can misinterpret, misunderstand and become very obsessed with something so they can be completely wrong about something. This will get them in trouble and give you plenty of ideas.

Example: If someone's in a room which there's nothing to see but fail a perception test, tell them they have a gut feeling this room is important. If they succeed tell them it's not important.
And in this time they could be discovered, attacked or lose a good opportunity. This would give you time to move NPCs, create situations and everything. It depends on your history.