[1.1.X] Fixed #11872 -- Instantiate the correct model in BaseInlineFormSet.__init__ when instance is None. Thanks tobias.

Backport of [11688] from trunk

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@11689 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/forms/models.py

@@ -709,7 +709,7 @@ class BaseInlineFormSet(BaseModelFormSet):
                  save_as_new=False, prefix=None):
         from django.db.models.fields.related import RelatedObject
         if instance is None:
-            self.instance = self.model()
+            self.instance = self.fk.rel.to()
         else:
             self.instance = instance
         self.save_as_new = save_as_new

tests/regressiontests/model_formsets_regress/tests.py

@@ -140,3 +140,13 @@ class InlineFormsetTests(TestCase):
             self.assertEqual(manager[1]['name'], 'Terry Gilliam')
         else:
             self.fail('Errors found on formset:%s' % form_set.errors)
+
+    def test_formset_with_none_instance(self):
+        "A formset with instance=None can be created. Regression for #11872"
+        Form = modelform_factory(User)
+        FormSet = inlineformset_factory(User, UserSite)
+
+        # Instantiate the Form and FormSet to prove
+        # you can create a formset with an instance of None
+        form = Form(instance=None)
+        formset = FormSet(instance=None)