docs: def changelist_view(self, request, extra_context=None):
          """
          If we only have a single preference object redirect to it,
          otherwise display listing.
          """
          model = self.model
          if model.objects.all().count() > 1:
              return super(HTMLSitemapAdmin, self).changelist_view(request)
          else:
              obj = model.singleton.get()
              return redirect(reverse('admin:jmbo_sitemap_%s_change' % \
                      model._meta.module_name, args=(obj.id,)))