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

      for(int i=0;i<batchSize;++i) {
        if (!isNull[i]) {
          if (myagg.isNull) {
            myagg.sum = 0;
            myagg.isNull = false;
          }
          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