I think you can do some cool things when you set classes. A colon `:` indicates 'else'. 

    {%
      set classes = [
        item.is_expanded ? 'is-expanded' : 'not-expanded',
        item.is_collapsed ? 'is-collapsed' : 'not-collapsed',
        item.in_active_trail ? 'active',
        item.below ? 'has-children': 'no-children
      ]
    %}