private void iterateHasNullsSelectionWithAggregationSelection(
      VectorAggregationBufferRow[] aggregationBufferSets,
      int aggregateIndex,
      TimestampColumnVector inputVector,
      int batchSize,
      int[] selection,
      boolean[] isNull) {

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