presto-main/src/main/java/io/prestosql/operator/OuterLookupSource.java/OuterLookupSource/OuterLookupSource
class OuterLookupSource:    private OuterLookupSource(LookupSource lookupSource, OuterPositionTracker outerPositionTracker)
    {
        this.lookupSource = requireNonNull(lookupSource, "lookupSource is null");
        this.outerPositionTracker = requireNonNull(outerPositionTracker, "outerPositionTracker is null");
    }