def pubsub(nid=nil)
      node_jid = if nid
                   JID.new(jid.node, jid.domain, nid)
                 else
                   jid.to_s
                 end
      PubSub.new(connection, node_jid)
    end
def pubsub(nid=nil)
      node_jid = if nid
                   JID.new(jid.node, jid.domain, nid)
                 else
                   jid.to_s
                 end
      PubSub.new(connection, node_jid)
    end
returns a PubSub entity with same bare jid
 accepts an optional node-id