NPE in Fetcher under load

2017-06-14 00:24:53,795 [INFO] [Dispatcher thread {Central}] |HistoryEventHandler.criticalEvents|: [HISTORY][DAG:dag_1490656001509_5009_1][Event:TASK_ATTEMPT_FINISHED]: vertexName=Reducer 36, taskAttemptId=attempt_1490656001509_5009_1_15_000013_0, creationTime=1497414223481, allocationTime=1497414290240, startTime=1497414290240, finishTime=1497414293795, timeTaken=3555, status=FAILED, taskFailureType=NON_FATAL, errorEnum=INPUT_READ_ERROR, diagnostics=Error: Error while running task ( failure ) : java.lang.NullPointerException
        at org.apache.tez.runtime.library.common.shuffle.Fetcher.fetchInputs(Fetcher.java:914)
        at org.apache.tez.runtime.library.common.shuffle.Fetcher.doHttpFetch(Fetcher.java:599)
        at org.apache.tez.runtime.library.common.shuffle.Fetcher.doHttpFetch(Fetcher.java:486)
        at org.apache.tez.runtime.library.common.shuffle.Fetcher.callInternal(Fetcher.java:284)
        at org.apache.tez.runtime.library.common.shuffle.Fetcher.callInternal(Fetcher.java:76)
        at org.apache.tez.common.CallableWithNdc.call(CallableWithNdc.java:36)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)
, errorMessage=Fetch failed:java.lang.NullPointerException
        at org.apache.tez.runtime.library.common.shuffle.Fetcher.fetchInputs(Fetcher.java:914)
        at org.apache.tez.runtime.library.common.shuffle.Fetcher.doHttpFetch(Fetcher.java:599)
        at org.apache.tez.runtime.library.common.shuffle.Fetcher.doHttpFetch(Fetcher.java:486)
        at org.apache.tez.runtime.library.common.shuffle.Fetcher.callInternal(Fetcher.java:284)
        at org.apache.tez.runtime.library.common.shuffle.Fetcher.callInternal(Fetcher.java:76)
        at org.apache.tez.common.CallableWithNdc.call(CallableWithNdc.java:36)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)