what is the correct way to add a class to `knp_menu's` root element `<ul>` with twig?

i tried a lot of things:

1.

```
{{ knp_menu_render('main', {'class': 'foo'}) }}

```

2.

```
{{ knp_menu_render('main', {'attributes': {'class': 'foo'}}) }}

```

3.

```
{{ knp_menu_render('main', {'listAttributes': {'class': 'foo'}}) }}

```

4.

```
{{ knp_menu_render('main', {'attributes': {'listAttributes': {'class': 'foo'}}}) }}

```

none of them worked