@SuppressWarnings("unchecked")
  @Override
  public RecordReader<NullWritable, NullWritable> getRecordReader(InputSplit split,
      JobConf conf, Reporter arg2) throws IOException {
    return new ZeroRowsRecordReader(conf, split);
  }
Same as OneNullRowInputFormat, but with 0 rows. There's no way to store smth like OperatorDesc
in InputFormat, so this is how it is. We could perhaps encode the number of null rows in the
null path. However, NullIF can be used without using NullFS, so that would not be possible.
ql/src/java/org/apache/hadoop/hive/ql/io/ZeroRowsInputFormat.java