M Train Accident @ City Hall

Just watching this on the news but they aren't giving out any details. According to channel 2 news, "An M train has hit a barrier at the City Hall train station. The situation is not serious."
Thats all they are saying, and the MTA site has no information as well. Anyone have info on exactly what happened?

looks like the TO slipped up and hit the bumper in the stub south of chambers street.. no passengers on board.

However, on another message board, a reliable source has noted that the entire consist of that train is now in storage pending final disposal. The cars were 4730-1, 4788-9, 4624-5, and 4818-9 (not necessarily in linking order).