public static void initOutputNullsToFalse(ColumnVector v, boolean isRepeating, boolean selectedInUse,
      int[] sel, int n) {
    if (v.isRepeating) {
      v.isNull[0] = false;
      return;
    }

    if (selectedInUse) {
      for (int j = 0; j != n; j++) {
        int i = sel[j];
        v.isNull[i] = false;
      }
    } else {
      Arrays.fill(v.isNull, 0, n, false);
    }
  }
Follow the convention that null decimal values are internally set to the smallest
positive value available. Prevents accidental zero-divide later in expression
evaluation.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/NullUtil.java