@Override
  public void assignRowColumn(VectorizedRowBatch batch, int batchIndex, int columnNum,
      AggregationBuffer agg) throws HiveException {

    Decimal64ColumnVector outputColVector = (Decimal64ColumnVector) batch.cols[columnNum];

    Aggregation myagg = (Aggregation) agg;
    if (myagg.isNull || myagg.isOverflowed) {
      outputColVector.noNulls = false;
      outputColVector.isNull[batchIndex] = true;
      return;
    }
    outputColVector.isNull[batchIndex] = false;

    outputColVector.vector[batchIndex] = myagg.sum;
  }
Value is explicitly (re)initialized in reset()
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/aggregates/VectorUDAFSumDecimal64.java