presto-parser/src/main/java/io/prestosql/sql/tree/DefaultTraversalVisitor.java/DefaultTraversalVisitor/visitWindowFrame
class DefaultTraversalVisitor:    @Override
    public R visitWindowFrame(WindowFrame node, C context)
    {
        process(node.getStart(), context);
        if (node.getEnd().isPresent()) {
            process(node.getEnd().get(), context);
        }

        return null;
    }