see ZkEventThread triggered when these is no broker change

see these errors in producer's log:

＝＝＝
[2014-05-17 08:38:59,983] ERROR Error handling event ZkEvent[Children of
/brokers/topics/test_device_updates changed sent to kafka
.producer.ZKBrokerPartitionInfo$BrokerTopicsListener [ at ] 1b0ec7cc]
(org.I0Itec.zkclient.ZkEventThread)
java.lang.NullPointerException
at org.I0Itec.zkclient.ZkConnection.readData(ZkConnection.java:103)
at org.I0Itec.zkclient.ZkClient$9.call(ZkClient.java:770)
at org.I0Itec.zkclient.ZkClient$9.call(ZkClient.java:766)
at
org.I0Itec.zkclient.ZkClient.retryUntilConnected(ZkClient.java:675)
at org.I0Itec.zkclient.ZkClient.readData(ZkClient.java:766)
at org.I0Itec.zkclient.ZkClient.readData(ZkClient.java:761)
at org.I0Itec.zkclient.ZkClient.readData(ZkClient.java:750)
at org.I0Itec.zkclient.ZkClient.readData(ZkClient.java:744)
at kafka.utils.ZkUtils$.readData(ZkUtils.scala:162)
at
kafka.producer.ZKBrokerPartitionInfo$$anonfun$1.apply$mcII$sp(ZKBrokerPartitionInfo.scala:40)
at
kafka.producer.ZKBrokerPartitionInfo$$anonfun$1.apply(ZKBrokerPartitionInfo.scala:40)
at
kafka.producer.ZKBrokerPartitionInfo$$anonfun$1.apply(ZKBrokerPartitionInfo.scala:40)
at
scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:233)
at
scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:233)
at
scala.collection.LinearSeqOptimized$class.foreach(LinearSeqOptimized.scala:59)
at scala.collection.immutable.List.foreach(List.scala:76)
at
scala.collection.TraversableLike$class.map(TraversableLike.scala:233)
at scala.collection.immutable.List.map(List.scala:76)
at
kafka.producer.ZKBrokerPartitionInfo$.kafka$producer$ZKBrokerPartitionInfo$$getBrokerPartitions(ZKBrokerPartitionInfo.s
cala:40)
at kafka.producer.ZKBrokerPartitionInfo$BrokerTopicsListener.
processNewBrokerInExistingTopic(ZKBrokerPartitionInfo.scala:3
09)
at kafka.producer.ZKBrokerPartitionInfo$BrokerTopicsListener.
handleChildChange(ZKBrokerPartitionInfo.scala:250)
at org.I0Itec.zkclient.ZkClient$7.run(ZkClient.java:568)
at org.I0Itec.zkclient.ZkEventThread.run(ZkEventThread.java:71)
[2014-05-17 09:21:39,558] ERROR Error handling event ZkEvent[Children of
/brokers/topics/test_mode_control changed sent to kafka.p
roducer.ZKBrokerPartitionInfo$BrokerTopicsListener [ at ] 1b0ec7cc]
(org.I0Itec.zkclient.ZkEventThread)
java.lang.NullPointerException
at org.I0Itec.zkclient.ZkConnection.exists(ZkConnection.java:95)
＝＝＝

After looking at the code of *ZKBrokerPartitionInfo*, seems that this
handleChildChange
will only be triggered when there is new broker added or removed from the
cluster, but we did not do that at that time, according to the monitoring,
we also didn't see any broker offline at that time.

so is there any other reason that will cause this error?

刘明敏 | mmLiu