presto-parser/src/main/java/io/prestosql/sql/tree/DefaultTraversalVisitor.java/DefaultTraversalVisitor/visitGroupBy
class DefaultTraversalVisitor:    @Override
    protected R visitGroupBy(GroupBy node, C context)
    {
        for (GroupingElement groupingElement : node.getGroupingElements()) {
            process(groupingElement, context);
        }

        return null;
    }