presto-main/src/main/java/io/prestosql/operator/OuterLookupSource.java/OuterLookupSource/OuterLookupSourceSupplier
class OuterLookupSource:        public OuterLookupSourceSupplier(Supplier<LookupSource> lookupSourceSupplier)
        {
            this.lookupSourceSupplier = requireNonNull(lookupSourceSupplier, "lookupSourceSupplier is null");
            this.outerPositionTracker = new OuterPositionTracker(lookupSourceSupplier);
        }