Squash Merge PR #379 for Django 2.2 support

Author: Asif Saif Uddin <auvipy@gmail.com>
Author: jeff <jeff@mighty.com>

polymorphic/formsets/utils.py

@@ -9,8 +9,8 @@ def add_media(dest, media):
     Optimized version of django.forms.Media.__add__() that doesn't create new objects.
     """
     if django.VERSION >= (2, 2):
-        dest._css_lists += media._css_lists
-        dest._js_lists += media._js_lists
+        dest._css_lists.extend(media._css_lists)
+        dest._js_lists.extend(media._js_lists)
     elif django.VERSION >= (2, 0):
         combined = dest + media
         dest._css = combined._css

polymorphic/tests/test_orm.py

@@ -226,7 +226,7 @@ class PolymorphicTests(TransactionTestCase):
     def test_defer_fields(self):
         self.create_model2abcd()
 
-        objects_deferred = Model2A.objects.defer('field1')
+        objects_deferred = Model2A.objects.defer('field1').order_by('id')
 
         self.assertNotIn('field1', objects_deferred[0].__dict__, 'field1 was not deferred (using defer())')
         self.assertRegex(repr(objects_deferred[0]),