presto-parser/src/main/java/io/prestosql/sql/tree/DefaultTraversalVisitor.java/DefaultTraversalVisitor/visitGroupingOperation
class DefaultTraversalVisitor:    @Override
    protected R visitGroupingOperation(GroupingOperation node, C context)
    {
        for (Expression columnArgument : node.getGroupingColumns()) {
            process(columnArgument, context);
        }

        return null;
    }