Failure to Yield: Contest a Failure to Yeild to Pedestrian

My question involves a traffic ticket from the state of: California

I received a ticket for failing to yeild to a pedestristrian. I was turning left at night after stopping 4 way stop. I waited for people to finish waking across the street and once they stepped on the curb I proceeded to enter the intersection. There was a cop also waiting to enter the intersection on the other side of the road.

After my turn the officer follow up behind me and pulled me over.

He said a pedestrian entered the crosswalk from on the right side while I was turning. Neither me or my wife saw anyone in the intersection while I completed my turn. The only thing I could think of was if someone stepped off the curb just as I entered the intersection as I would not have seen my direct right while finishing my turn. If someone did step off the curb at the time while I'm in the intersection shouldn't I finish my turn assuming I am also not putting he pedestrian at risk? I'm not sure and like I said we never saw any pedestrian in the crosswalk at the time.

How do I contest this?

Thank you
Cam

Failure to Yield: Contest a Failure to Yeild to Pedestrian