The 12-volt battery for the vehicle was depleted, so the vehicle had to be jump-started to run. I work for a repair facility (it was here for collision repairs, as far as I know unrelated to this issue) and since I was unfamiliar with the vehicle, I inadvertently turned it off before shifting into park. When I took my foot off the brake, the vehicle began to roll forward. I am not sure if the vehicle was in park, neutral, or even reverse (the gear I was in when I turned the vehicle off), but whatever gear it was, the vehicle kept rolling after it was turned off. I tried turning the vehicle back on to shift to park, but was unable to do so due to the depleted 12-volt battery. I tried hitting the park button anyway, and this did nothing. I then tried to engage the electronic parking brake, but this was also inoperative due to the lack of power. With each attempt, I tried briefly taking my foot off the brake, but each time it continued to roll forward. I then called my manager and asked him to jump start the vehicle so I could put it in park and engage the parking brake. No damage was done in this incident, nor was anyone hurt, but this lack of fail-safes to prevent the vehicle from moving after a loss of power is a significant design flaw and safety hazard. If I had not noticed the issue in time and gotten out, the vehicle could have rolled away and caused property damage or bodily injury to me or a bystander. To my knowledge, this is the only such incident with this vehicle, and I do not know whether it is specific to this particular vehicle or replicable in others of the same year make and model. There were no warning lights.