def muc(nick=nil)
      muc_jid = JID.new jid.node, jid.domain, nick
      Muc.new(connection, muc_jid)
    end
def muc(nick=nil)
      muc_jid = JID.new jid.node, jid.domain, nick
      Muc.new(connection, muc_jid)
    end
Generates a MUC entity from this entity.
 If the nick argument is null then the entity is the MUC itself.
 If the nick argument is present, then the entity is the user with
 the corresponding nickname.