docs: def slug_exists(self, request):
          """Check if given url slug exists.
  
          Check if slug given in query parameter ``name`` exists. Return
          ``True`` if slug already exists and ``False`` otherwise.
  
          """
          if not request.user.is_authenticated:
              return Response(status=status.HTTP_401_UNAUTHORIZED)
  
          if 'name' not in request.query_params:
              return Response({'error': 'Query parameter `name` must be given.'},
                              status=status.HTTP_400_BAD_REQUEST)
  
          queryset = self.get_queryset()
          slug_name = request.query_params['name']
          return Response(queryset.filter(slug__iexact=slug_name).exists())