code: public void doUnload(final Wave wave) {
          this.eventList = new ArrayList<>();
  
          final Collection<BallModel> list = new ArrayList<>(this.ballMap.values());
  
          for (final BallModel ballModel : list) {
              unregisterBall(ballModel);
          }
      }
docs: Unload the event list.
  
  @param wave the wave received