private void iterateNoSelectionNoNulls(
        Aggregation myagg,
        TimestampColumnVector inputVector,
        int batchSize) {
      if (myagg.isNull) {
        myagg.sum = 0;
        myagg.isNull = false;
      }

      for (int i=0;i<batchSize;++i) {
        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