presto-main/src/main/java/io/prestosql/sql/analyzer/StatementAnalyzer.java/Visitor/Visitor
class Visitor:        private Visitor(Optional<Scope> outerQueryScope, WarningCollector warningCollector)
        {
            this.outerQueryScope = requireNonNull(outerQueryScope, "outerQueryScope is null");
            this.warningCollector = requireNonNull(warningCollector, "warningCollector is null");
        }