same thing happened to me a few years back, he charged me with possession, (I signed the citation) and fought it in court, after over a year, finally got my day in court, told them the story, judge was like, you seroius? you're free to go.

so unless they tested you for THC in your system at the time of the traffic stop, they don't have a case.

it was pretty funny, my buddies got charged, did their community service, classes, etc, got all that stuff done with by the time I got my day in court.