private void iterateSelectionHasNulls(
        Aggregation myagg,
        TimestampColumnVector inputVector,
        int batchSize,
        boolean[] isNull,
        int[] selected) {

      for (int j=0; j< batchSize; ++j) {
        int i = selected[j];
        if (!isNull[i]) {
          if (myagg.isNull) {
            myagg.isNull = false;
            myagg.sum = 0;
          }
          myagg.sum += inputVector.getDouble(i);
        }
      }
    }
Value is explicitly (re)initialized in reset()
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/aggregates/VectorUDAFSumTimestamp.java