code: public static PublicKeysListElement fetchPubkeysList(XMPPConnection connection)
              throws InterruptedException, XMPPException.XMPPErrorException, PubSubException.NotAPubSubNodeException,
              PubSubException.NotALeafNodeException, SmackException.NotConnectedException, SmackException.NoResponseException {
          return fetchPubkeysList(connection, null);
      }
docs: Consult the public key metadata node and fetch a list of all of our published OpenPGP public keys.
  
  @see <a href="https://xmpp.org/extensions/xep-0373.html#discover-pubkey-list">
  XEP-0373 §4.3: Discovering Public Keys of a User</a>
  
  @param connection XMPP connection
  @return content of our metadata node.
  
  @throws InterruptedException if the thread gets interrupted.
  @throws XMPPException.XMPPErrorException in case of an XMPP protocol exception.
  @throws PubSubException.NotAPubSubNodeException in case the queried entity is not a PubSub node
  @throws PubSubException.NotALeafNodeException in case the queried node is not a {@link LeafNode}
  @throws SmackException.NotConnectedException in case we are not connected
  @throws SmackException.NoResponseException in case the server doesn't respond