code: def get_image_set(self):
          
          image_set_pk = self.kwargs.get("pk", None)
          if image_set_pk is None:
              return self.request.user.image_sets.create()
          return get_object_or_404(self.get_queryset(), pk=image_set_pk)
docs: Obtain existing ImageSet if `pk` is specified, otherwise
          create a new ImageSet for the user.