Ticket #6702: newforms_models_assert_isinstance.diff

django/newforms/models.py

@@ -250 +250 @@
             self.instance = opts.model()
             object_data = {}
         else:
+            assert isinstance(instance, opts.model), 'instance (%r)  must be an instance of %r' % (
+                instance, opts.model)
             self.instance = instance
             object_data = model_to_dict(instance, opts.fields, opts.exclude)
         # if initial was provided, it should override the values from instance