Room Subject/Topic

Hi,

How can i get the subject of a particular room. I;m using this code but is not working :

var _room:Room;

_room = new Room();

_room.roomJID=new JID(data.jid);

_room.enableAutoUpdate();

trace ("room list data "+_room.roomJID);

trace ("room list data "+_room.fullRoomName);

trace ("room list data "+_room.role);

trace("subject is: "+_room.subject);

I need to fiind the topic of the room before joining .

Thank you