Asteroid
Ну фразы вроде "они зашли в пустой класс" в книгах, емнип, встречаются неоднократно.
"When they were a floor up from Lockhart’s office, they turned into an empty classroom and closed the door quietly behind them." (ГПиТК)
"He nodded towards an empty classroom to the left of the one-eyed statue. Harry followed Fred and George inside. George closed the door quietly and then turned, beaming, to look at Harry." (ГПиУА)