presto-main/src/main/java/io/prestosql/cost/CostCalculatorUsingExchanges.java/CostCalculatorUsingExchanges/CostEstimator
class CostCalculatorUsingExchanges:        CostEstimator(StatsProvider stats, CostProvider sourcesCosts, TypeProvider types, TaskCountEstimator taskCountEstimator)
        {
            this.stats = requireNonNull(stats, "stats is null");
            this.sourcesCosts = requireNonNull(sourcesCosts, "sourcesCosts is null");
            this.types = requireNonNull(types, "types is null");
            this.taskCountEstimator = requireNonNull(taskCountEstimator, "taskCountEstimator is null");
        }