Is that supposed to be a serious question? Of course Nevada has stoplights. There are nearly two million people in the Las Vegas area and around two hundred fifty thousand people in the Reno/Sparks area. Then there are LOTS of smaller towns with populations as low as twenty five up to fifty thousand. Sure there are huge amounts of unpopulated or sparsely populated areas but that's not much different than the central valley in California as an example.
Boom - it wasn't serious! It was meant to spark discussion on how on earth do these cars handle trickier aspects of driving on unmodified grids, such as traffic lights.
I would assume since they've already logged lots of hours driving around CA that the various sensors and cameras can already detect traffic lights. On that same line of thought I'd love to know how they adjust for speed in construction zones with non standard speed limit signs, the randomness of other drivers etc.