public static void setNullOutputEntriesColScalar(
      ColumnVector v, boolean selectedInUse, int[] sel, int n) {
    if (v instanceof DoubleColumnVector) {

      // No need to set null data entries because the input NaN values
      // will automatically propagate to the output.
      return;
    } else if (v instanceof LongColumnVector) {
      setNullDataEntriesLong((LongColumnVector) v, selectedInUse, sel, n);
    } else if (v instanceof TimestampColumnVector){
      setNullDataEntriesTimestamp((TimestampColumnVector) v, selectedInUse, sel, n);
    }
  }
Set the data value for all NULL entries to the designated NULL_VALUE.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/NullUtil.java