  
      def _add_to_cache(self, using, ct):
          """Insert a ContentType into the cache."""
          model = ct.model_class()
          key = (model._meta.app_label, model._meta.object_name.lower())
          self.__class__._cache.setdefault(using, {})[key] = ct
          self.__class__._cache.setdefault(using, {})[ct.id] = ct
  
  @python_2_unicode_compatible
  class ContentType(models.Model):
 
</s> remove         key = (opts.app_label, opts.object_name.lower())
 </s> add         key = (opts.app_label, opts.model_name) </s> remove                 model = opts.object_name.lower(),
 </s> add                 model = opts.model_name, </s> remove                 needed_models.add(opts.object_name.lower())
 </s> add                 needed_models.add(opts.model_name) </s> remove                 model=opts.object_name.lower(),
 </s> add                 model=opts.model_name, </s> remove         response['X-Object-Type'] = "%s.%s" % (model._meta.app_label, model._meta.object_name.lower())
 </s> add         response['X-Object-Type'] = "%s.%s" % (model._meta.app_label, model._meta.model_name)
        key = (model._meta.app_label, model._meta.model_name)
  
      def _add_to_cache(self, using, ct):
          """Insert a ContentType into the cache."""
          model = ct.model_class()
        key = (model._meta.app_label, model._meta.model_name)
          self.__class__._cache.setdefault(using, {})[key] = ct
          self.__class__._cache.setdefault(using, {})[ct.id] = ct
  
  @python_2_unicode_compatible
  class ContentType(models.Model):
keep keep keep keep replace keep keep keep keep keep
 Fixed #19689 -- Renamed `Model._meta.module_name` to `model_name`. 
django/contrib/contenttypes/models.py