presto-main/src/main/java/io/prestosql/operator/MergeOperator.java/MergeOperator/MergeOperator
class MergeOperator:    public MergeOperator(
            OperatorContext operatorContext,
            PlanNodeId sourceId,
            ExchangeClientSupplier exchangeClientSupplier,
            PagesSerde pagesSerde,
            PageWithPositionComparator comparator,
            List<Integer> outputChannels,
            List<Type> outputTypes)
    {
        this.operatorContext = requireNonNull(operatorContext, "operatorContext is null");
        this.sourceId = requireNonNull(sourceId, "sourceId is null");
        this.exchangeClientSupplier = requireNonNull(exchangeClientSupplier, "exchangeClientSupplier is null");
        this.pagesSerde = requireNonNull(pagesSerde, "pagesSerde is null");
        this.comparator = requireNonNull(comparator, "comparator is null");
        this.outputChannels = requireNonNull(outputChannels, "outputChannels is null");
        this.outputTypes = requireNonNull(outputTypes, "outputTypes is null");
    }