presto-main/src/main/java/io/prestosql/sql/planner/SymbolsExtractor.java/SymbolsExtractor/QualifiedNameBuilderVisitor
class SymbolsExtractor:        private QualifiedNameBuilderVisitor(Set<NodeRef<Expression>> columnReferences)
        {
            this.columnReferences = requireNonNull(columnReferences, "columnReferences is null");
        }