public void setEmptyDate(Date emptyDate) {
        // Do nothing if old value is same as new value
        if (this.emptyDate == emptyDate) {
            return;
        }
        this.emptyDate = emptyDate;
        MUCPersistenceManager.updateRoomEmptyDate(this);
    }
Sets the date when the last occupant left the room. A null value means that there are
occupants in the room at the moment.

@param emptyDate the date when the last occupant left the room or null if there are occupants in the room (can be {@code null}).
xmppserver/src/main/java/org/jivesoftware/openfire/muc/MUCRoom.java