[1.8.x] Fixed #24377 -- Fixed model inline formsets with primary key's that have defaults.

Backport of 1306cd1e8a from master

tests/model_formsets/test_uuid.py

@@ -0,0 +1,32 @@
+from django.forms.models import inlineformset_factory
+from django.test import TestCase
+
+from .models import UUIDPKChild, UUIDPKParent
+
+
+class InlineFormsetTests(TestCase):
+    def test_inlineformset_factory_nulls_default_pks(self):
+        """
+        #24377 - If we're adding a new object, a parent's auto-generated pk
+        from the model field default should be ignored as it's regenerated on
+        the save request.
+        """
+        FormSet = inlineformset_factory(UUIDPKParent, UUIDPKChild, fields='__all__')
+        formset = FormSet()
+        self.assertIsNone(formset.forms[0].fields['parent'].initial)
+
+    def test_inlineformset_factory_ignores_default_pks_on_submit(self):
+        """
+        #24377 - Inlines with a model field default should ignore that default
+        value to avoid triggering validation on empty forms.
+        """
+        FormSet = inlineformset_factory(UUIDPKParent, UUIDPKChild, fields='__all__')
+        formset = FormSet({
+            'uuidpkchild_set-TOTAL_FORMS': 3,
+            'uuidpkchild_set-INITIAL_FORMS': 0,
+            'uuidpkchild_set-MAX_NUM_FORMS': '',
+            'uuidpkchild_set-0-name': 'Foo',
+            'uuidpkchild_set-1-name': '',
+            'uuidpkchild_set-2-name': '',
+        })
+        self.assertTrue(formset.is_valid())