The police officer hits their lights, pulling over the vehicle in front of them, walks up to the driver's window, and ... there's no one inside.It prompts a question that can only be asked in the handful of U.S. cities that allow autonomous vehicles: What happens when an officer stops a car and there's no driver?That question, accompanied by a photograph of a Waymo autonomous vehicle that had been pulled over in central Phoenix on June 19, was posted on the social media website Reddit last month...