Github user XuPingyong commented on the issue:
    @greghogan, if the object passed to nextRecord may be reused internally 
by the InputFormat, do the similar cases need to  be re-considered?
    In ``:
                  OT reuse = serializer.createInstance();
                // as long as there is data to read
                while (!this.taskCanceled && !format.reachedEnd()) {
                    OT returned;
                    if ((returned = format.nextRecord(reuse)) != null) {
    And in many batch drivers:
                  final MutableObjectIterator<T> in = taskContext.getInput(0);
                  T value = serializer.createInstance();
                  while (running && (value = != null) {
    In my opinion:
         1.  `Null` records are meaningless, but `null` is meaningful for input 
or format which means the end. If a user only call `InputFormat#nextRecord` 
without `InputFormat#reachedEnd`, only `null` can be returned. 
         2.  The returned object of `InputFormat#nextRecord` should not need to 
be considered that it may be passed again. If a immutable object is returned, 
an exception will be thrown  when it is reused again in 
    @greghogan, could you please offer some cases that the object passed to 
nextRecord can be reused internally by the InputFormat?  Thanks.

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