CheckPointing in giraph-1.1.0

[Vissu Viswanath]

Hi,
      My giraph job is working fine. But, when I introduce
conf.setCheckpointFrequency(4), it is failing. The error I am getting is:

java.lang.IllegalStateException: run: Caught an unrecoverable exception null
        at org.apache.giraph.graph.GraphMapper.run(GraphMapper.java:101)
        at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:763)
        at org.apache.hadoop.mapred.MapTask.run(MapTask.java:369)
        at org.apache.hadoop.mapred.Child$4.run(Child.java:259)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:416)
        at 
org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1059)
        at org.apache.hadoop.mapred.Child.main(Child.java:253)
Caused by: java.lang.NullPointerException
        at 
org.apache.giraph.utils.WritableUtils.writeVertexToDataOutput(WritableUtils.java:577)
        at 
org.apache.giraph.partition.SimplePartition.write(SimplePartition.java:141)
        at 
org.apache.giraph.worker.BspServiceWorker.storeCheckpoint(BspServiceWorker.java:1127)
        at 
org.apache.giraph.graph.GraphTaskManager.checkSuperstepRestarted(GraphTaskManager.java:773)
        at 
org.apache.giraph.graph.GraphTaskManager.execute(GraphTaskManager.java:271)
        at org.apache.giraph.graph.GraphMapper.run(GraphMapper.java:91)
        ... 7 more

Can anyone help me in fixing this?

Thanks,
Vish