code: @SuppressWarnings("unchecked")
      @Override
      public Boolean execute() {
          User sfsUser = CommandUtil.getSfsUser(userToJoin, api);
          Room sfsRoomToJoin = CommandUtil.getSfsRoom(roomToJoin, extension);
          Room sfsRoomToLeave = (roomToLeave != null)
                  ? CommandUtil.getSfsRoom(roomToLeave, extension) : null;
          sfsRoomToLeave = (sfsRoomToLeave == null) 
                  ? sfsUser.getLastJoinedRoom() : sfsRoomToLeave;
          try {
              api.joinRoom(sfsUser, 
                      sfsRoomToJoin, 
                      password, 
                      asSpectator, 
                      sfsRoomToLeave, 
                      fireClientEvent, 
                      fireServerEvent);
          } catch (SFSJoinRoomException e) {
              throw new IllegalStateException(e);
          }
          return Boolean.TRUE;
      }
docs: /* (non-Javadoc)
  @see com.lagente.core.command.BaseCommand#execute()