code: def parent_link
        link = {}
        if collection_hierarchy.length > 1
          parent_name = collection_hierarchy[-2].class.name.downcase
          link[parent_name] = {
            href: @controller.polymorphic_url(collection_hierarchy[0..-2])
          }
        end
        link
      end
docs: Internal: Returns a Hash with a link to the parent of the collection, if
   it exists, or an empty Hash otherwise.