consumer null pointer exception

[Kane Kane]

I've got the following exception running produce/consume loop for several
hours,
that was just single exception, but during that time both producers and
consumers slowed down a lot. After that looks like everything works fine,
though i have
suspicion some messages were lost.
Can anyone explain what it might be?

WARN  consumer.ZookeeperConsumerConnector -
[group2_kafka-001.sendgrid.net-1383289
653031-b02bae92], exception during commitOffsets
java.lang.NullPointerException
        at
org.I0Itec.zkclient.ZkConnection.writeDataReturnStat(ZkConnection.java:115)
        at org.I0Itec.zkclient.ZkClient$10.call(ZkClient.java:817)
        at
org.I0Itec.zkclient.ZkClient.retryUntilConnected(ZkClient.java:675)
        at
org.I0Itec.zkclient.ZkClient.writeDataReturnStat(ZkClient.java:813)
        at org.I0Itec.zkclient.ZkClient.writeData(ZkClient.java:808)
        at org.I0Itec.zkclient.ZkClient.writeData(ZkClient.java:777)
        at kafka.utils.ZkUtils$.updatePersistentPath(Unknown Source)
        at
kafka.consumer.ZookeeperConsumerConnector$$anonfun$commitOffsets$3$$anonfun$apply$5.apply(Unknown
Source)
        at
kafka.consumer.ZookeeperConsumerConnector$$anonfun$commitOffsets$3$$anonfun$apply$5.apply(Unknown
Source)
        at scala.collection.Iterator$class.foreach(Iterator.scala:727)
        at scala.collection.AbstractIterator.foreach(Iterator.scala:1157)
        at
scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
        at scala.collection.AbstractIterable.foreach(Iterable.scala:54)
        at
kafka.consumer.ZookeeperConsumerConnector$$anonfun$commitOffsets$3.apply(Unknown
Source)
        at
kafka.consumer.ZookeeperConsumerConnector$$anonfun$commitOffsets$3.apply(Unknown
Source)
        at
scala.collection.TraversableLike$WithFilter$$anonfun$foreach$1.apply(TraversableLike.scala:772)
        at scala.collection.Iterator$class.foreach(Iterator.scala:727)
        at kafka.utils.Pool$$anon$1.foreach(Unknown Source)
        at
scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
        at kafka.utils.Pool.foreach(Unknown Source)
        at
scala.collection.TraversableLike$WithFilter.foreach(TraversableLike.scala:771)
        at kafka.consumer.ZookeeperConsumerConnector.commitOffsets(Unknown
Source)