gistfile1.txt

2013-09-19 15:26:37,309 ERROR: org.graylog2.indexer.Indexer - Could not read name of ES node.
java.lang.NullPointerException
  at org.graylog2.indexer.Indexer.nodeIdToHostName(Indexer.java:152)
	at org.graylog2.indexer.DeflectorInformation.getShardInformation(DeflectorInformation.java:108)
	at org.graylog2.indexer.DeflectorInformation.getIndexInformation(DeflectorInformation.java:94)
	at org.graylog2.indexer.DeflectorInformation.getAsDatabaseObject(DeflectorInformation.java:74)
	at org.graylog2.periodical.DeflectorInformationWriterThread.run(DeflectorInformationWriterThread.java:67)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
	at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:351)
	at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:178)
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178)
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:724)

this is the location
https://github.com/Graylog2/graylog2-server/blob/020/graylog2-server/src/main/java/org/graylog2/indexer/Indexer.java#L147

the NPE is from r.getNodesMap() being empty, which never happened before (and does not happen with 0.90.5 as the server)
the client is a 0.90.5 nodeclient.