code: def _prepare_template(self, obj, needs_request=False):
          
          if self.instance_name is None and self.template_name is None:
              raise SearchFieldError("This field requires either its instance_name variable to be populated or an explicit template_name in order to load the correct template.")
  
          if self.template_name is not None:
              template_names = self.template_name
  
              if not isinstance(template_names, (list, tuple)):
                  template_names = [template_names]
          else:
              template_names = ['search/indexes/%s/%s_%s.txt' % (obj._meta.app_label, obj._meta.module_name, self.instance_name)]
  
          t = loader.select_template(template_names)
          ctx = {'object': obj}
          if needs_request:
              request = rf.get("/")
              request.session = {}
              ctx['request'] = request
          return t.render(Context(ctx))
docs: This is a copy of CharField.prepare_template, except that it adds a fake
          request to the context, which is mainly needed to render CMS placeholders