This is an excerpt from LocalOutgoingServerSession#returnErrorToSender(Packet packet):
if (packet instanceof IQ) {
IQ reply = new IQ();
reply.setID(packet.getID());
reply.setTo(packet.getFrom());
reply.setFrom(packet.getTo());
reply.setChildElement(((IQ) packet).getChildElement().createCopy());
reply.setError(PacketError.Condition.remote_server_not_found);
routingTable.routePacket(reply.getTo(), reply, true);
}
This code will throw a NullPointerException if the IQ that is being replied to doesn’t have a child element (this is valid for IQ types ‘result’ and ‘error’). It is in any case a violation of RFC-3920 to respond with an ‘error’ stanza to an ‘error’ or ‘result’ stanza.
Something like this should fix the problem. It does no longer notify the sender that a problem occurred though:
if (packet instanceof IQ) {
IQ iq = (IQ) packet;
if (iq.getType().equals(IQ.Type.result) || iq.getType().equals(IQ.Type.error)) {
Log.warn("XMPP specs forbid us to respond with an IQ error to: " + packet);
return;
}
IQ reply = new IQ();
reply.setID(packet.getID());
reply.setTo(packet.getFrom());
reply.setFrom(packet.getTo());
reply.setChildElement(iq.getChildElement().createCopy());
reply.setError(PacketError.Condition.remote_server_not_found);
routingTable.routePacket(reply.getTo(), reply, true);
}