A lot of the time cops are just as nervous as the people they pull over considering at any second the person they are pulling over could pull a gun on them because they are carrying something else that is illegal. Even if you do have weed on you if you act nervous or like an asshole to a cop the results aren't going to be so good. If you just comply and talk to the cop respectably you should get off clean. If you are being pulled over its most likely cause of speeding or some other thing wrong with your car so there is no reason to let them catch you for possesion when they would just give you a ticket.