Null pointer exception in JobTracker when the task tracker is not yet resolved

2008-06-17 13:29:56,711 INFO org.apache.hadoop.mapred.JobTracker: Got heartbeat from: xxx (initialContact: false acceptNewTasks: true) with responseId: 0
2008-06-17 13:29:56,711 INFO org.apache.hadoop.ipc.Server: IPC Server handler 7 on 123, call heartbeat(org.apache.hadoop.mapred.TaskTrackerStatus@123, true, true, -1) from xxx error: java.io.IOException: java.lang.NullPointerException
java.io.IOException: java.lang.NullPointerException
at org.apache.hadoop.mapred.JobTracker.getParentNode(JobTracker.java:1327)
at org.apache.hadoop.mapred.JobInProgress.findNewMapTask(JobInProgress.java:1142)
at org.apache.hadoop.mapred.JobInProgress.obtainNewMapTask(JobInProgress.java:685)
at org.apache.hadoop.mapred.JobTracker.getNewTaskForTaskTracker(JobTracker.java:1708)
at org.apache.hadoop.mapred.JobTracker.heartbeat(JobTracker.java:1431)
at sun.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:452)
at org.apache.hadoop.ipc.Server$Handler.run(Server.java:888)

Looks like a corner case. This happens when the task tracker just joins the JT and asks for a task to run. In a case where the task tracker is not yet resolved, this can lead to null pointer exception. Remember that the task trackers are added to separate queue and resolved by a separate thread i.e there is no forced resolution for task trackers. There is no side effect of this bug since the task tracker will try again and also the job runs to completion.