presto-main/src/main/java/io/prestosql/sql/planner/optimizations/OptimizeMixedDistinctAggregations.java/OptimizeMixedDistinctAggregations/Optimizer
class OptimizeMixedDistinctAggregations:        private Optimizer(PlanNodeIdAllocator idAllocator, SymbolAllocator symbolAllocator, Metadata metadata)
        {
            this.idAllocator = requireNonNull(idAllocator, "idAllocator is null");
            this.symbolAllocator = requireNonNull(symbolAllocator, "symbolAllocator is null");
            this.metadata = requireNonNull(metadata, "metadata is null");
        }