@Override
  public void aggregateInputSelection(
    VectorAggregationBufferRow[] aggregationBufferSets,
    int aggregateIndex,
    VectorizedRowBatch batch) throws HiveException {

    int batchSize = batch.size;

    if (batchSize == 0) {
      return;
    }

    inputExpression.evaluate(batch);

    Decimal64ColumnVector inputVector =
        (Decimal64ColumnVector) batch.cols[
            this.inputExpression.getOutputColumnNum()];

    long[] vector = inputVector.vector;

    if (inputVector.noNulls) {
      if (inputVector.isRepeating) {
        iterateNoNullsRepeatingWithAggregationSelection(
          aggregationBufferSets, aggregateIndex,
          vector[0], batchSize);
      } else {
        if (batch.selectedInUse) {
          iterateNoNullsSelectionWithAggregationSelection(
            aggregationBufferSets, aggregateIndex,
            vector, batch.selected, batchSize);
        } else {
          iterateNoNullsWithAggregationSelection(
            aggregationBufferSets, aggregateIndex,
            vector, batchSize);
        }
      }
    } else {
      if (inputVector.isRepeating) {
        iterateHasNullsRepeatingWithAggregationSelection(
          aggregationBufferSets, aggregateIndex,
          vector[0], batchSize, inputVector.isNull);
      } else {
        if (batch.selectedInUse) {
          iterateHasNullsSelectionWithAggregationSelection(
            aggregationBufferSets, aggregateIndex,
            vector, batchSize, batch.selected, inputVector.isNull);
        } else {
          iterateHasNullsWithAggregationSelection(
            aggregationBufferSets, aggregateIndex,
            vector, batchSize, inputVector.isNull);
        }
      }
    }
  }
Value is explicitly (re)initialized in reset()
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/aggregates/VectorUDAFSumDecimal64ToDecimal.java