NoSuchElementException occurs during assigning the leaf tasks

2014-03-17 15:37:30,982 INFO  planner.PhysicalPlannerImpl (PhysicalPlannerImpl.java:createInMemoryHashAggregation(898)) - The planner chooses [Hash Aggregation]
2014-03-17 15:37:31,061 INFO  util.RackResolver (RackResolver.java:coreResolve(109)) - Resolved 192.168.0.205 to /default-rack
2014-03-17 15:37:31,061 INFO  master.DefaultTaskScheduler (DefaultTaskScheduler.java:allocateRackTask(701)) - Assigned Local/Rack/Total: (0/2/2), Locality: 0.00%, Rack host: 192.168.0.205
Exception in thread "Thread-16" java.util.NoSuchElementException
  at java.util.ArrayList$Itr.next(ArrayList.java:794)
  at org.apache.tajo.master.DefaultTaskScheduler$ScheduledRequests.assignToLeafTasks(DefaultTaskScheduler.java:716)
  at org.apache.tajo.master.DefaultTaskScheduler.schedule(DefaultTaskScheduler.java:162)
  at org.apache.tajo.master.DefaultTaskScheduler$1.run(DefaultTaskScheduler.java:101)
2014-03-17 15:37:31,068 INFO  worker.TaskRunner (TaskRunner.java:run(374)) - Accumulated Received Task: 1
2014-03-17 15:37:31,068 INFO  worker.TaskRunner (TaskRunner.java:run(383)) - Initializing: ta_1395038211889_0001_000001_000001_00
2014-03-17 15:37:31,096 INFO  worker.TaskAttemptContext (TaskAttemptContext.java:setState(110)) - Query status of ta_1395038211889_0001_000001_000001_00 is changed to TA_PENDING