Failed to route packet Error with chat messages

We have 2 clustered openfire servers, version 3.9.3.

We keep seeing an exception on the logs but we haven’t been able to find out what is causing it (I ofuscated some private info). Any idea on what could be the problem?

014.10.30 21:19:18 org.jivesoftware.openfire.MessageRouter - Failed to route packet: 2014-10-30 21:19:23.254

java.lang.NullPointerException

at org.jivesoftware.openfire.spi.RoutingTableImpl$2.compare(RoutingTableImpl.java: 596)

at org.jivesoftware.openfire.spi.RoutingTableImpl$2.compare(RoutingTableImpl.java: 594)

at java.util.TimSort.countRunAndMakeAscending(Unknown Source)

at java.util.TimSort.sort(Unknown Source)

at java.util.TimSort.sort(Unknown Source)

at java.util.Arrays.sort(Unknown Source)

at java.util.Collections.sort(Unknown Source)

at org.jivesoftware.openfire.spi.RoutingTableImpl.routeToBareJID(RoutingTableImpl. java:594)

at org.jivesoftware.openfire.spi.RoutingTableImpl.routeToLocalDomain(RoutingTableI mpl.java:293)

at org.jivesoftware.openfire.spi.RoutingTableImpl.routePacket(RoutingTableImpl.jav a:238)

at org.jivesoftware.openfire.MessageRouter.route(MessageRouter.java:138)

at org.jivesoftware.openfire.spi.PacketRouterImpl.route(PacketRouterImpl.java:80)

at org.jivesoftware.openfire.net.StanzaHandler.processMessage(StanzaHandler.java:3 66)

at org.jivesoftware.openfire.net.ClientStanzaHandler.processMessage(ClientStanzaHa ndler.java:107)

at org.jivesoftware.openfire.net.StanzaHandler.process(StanzaHandler.java:220)

at org.jivesoftware.openfire.net.StanzaHandler.process(StanzaHandler.java:187)

at org.jivesoftware.openfire.nio.ConnectionHandler.messageReceived(ConnectionHandl er.java:181)

at org.apache.mina.common.support.AbstractIoFilterChain$TailFilter.messageReceived (AbstractIoFilterChain.java:570)

at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(Ab stractIoFilterChain.java:299)

at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilt erChain.java:53)

at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceive d(AbstractIoFilterChain.java:648)

at org.apache.mina.common.IoFilterAdapter.messageReceived(IoFilterAdapter.java:80)

at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(Ab stractIoFilterChain.java:299)

at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilt erChain.java:53)

at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceive d(AbstractIoFilterChain.java:648)

at org.apache.mina.filter.codec.support.SimpleProtocolDecoderOutput.flush(SimplePr otocolDecoderOutput.java:58)

at org.apache.mina.filter.codec.ProtocolCodecFilter.messageReceived(ProtocolCodecF ilter.java:185)

at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(Ab stractIoFilterChain.java:299)

at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilt erChain.java:53)

at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceive d(AbstractIoFilterChain.java:648)

at org.apache.mina.filter.executor.ExecutorFilter.processEvent(ExecutorFilter.java :239)

at org.apache.mina.filter.executor.ExecutorFilter$ProcessEventsRunnable.run(Execut orFilter.java:283)

at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)

at org.apache.mina.util.NamePreservingRunnable.run(NamePreservingRunnable.java:51)

at java.lang.Thread.run(Unknown Source)