From 74929c20552b247df14bbcfdb8b714eb3124e9aa Mon Sep 17 00:00:00 2001
From: Tocho Tochev <tocho@tochev.net>
Date: Tue, 25 Jul 2017 13:31:57 +0300
Subject: [PATCH] Fix reset of .select_related

---
 modeltranslation/manager.py     |  5 ++++-
 modeltranslation/tests/tests.py | 15 +++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/modeltranslation/manager.py b/modeltranslation/manager.py
index 08d3adc..0d41d4b 100644
--- a/modeltranslation/manager.py
+++ b/modeltranslation/manager.py
@@ -255,7 +255,10 @@ class MultilingualQuerySet(models.query.QuerySet):
         # new_args = append_lookup_keys(self.model, fields)
         new_args = []
         for key in fields:
-            new_args.append(rewrite_lookup_key(self.model, key))
+            if key is None:
+                new_args.append(None)
+            else:
+                new_args.append(rewrite_lookup_key(self.model, key))
         return super(MultilingualQuerySet, self).select_related(*new_args, **kwargs)
 
     # This method was not present in django-linguo
diff --git a/modeltranslation/tests/tests.py b/modeltranslation/tests/tests.py
index ce7d92c..678d59f 100644
--- a/modeltranslation/tests/tests.py
+++ b/modeltranslation/tests/tests.py
@@ -2966,6 +2966,21 @@ class TestManager(ModeltranslationTestBase):
         o.title = "bla"
         self.assertEqual(o.title, "bla")
 
+    def test_select_related(self):
+        test = models.TestModel.objects.create(title_de='title_de', title_en='title_en')
+        with auto_populate('all'):
+            models.ForeignKeyModel.objects.create(untrans=test)
+
+        fk_qs = models.ForeignKeyModel.objects.all()
+        self.assertNotIn('_untrans_cache', fk_qs[0].__dict__)
+        self.assertIn('_untrans_cache', fk_qs.select_related('untrans')[0].__dict__)
+        self.assertNotIn(
+            '_untrans_cache',
+            fk_qs.select_related('untrans').select_related(None)[0].__dict__
+        )
+        # untrans is nullable so not included when select_related=True
+        self.assertNotIn('_untrans_cache', fk_qs.select_related()[0].__dict__)
+
     def test_translation_fields_appending(self):
         from modeltranslation.manager import append_lookup_keys, append_lookup_key
         self.assertEqual(set(['untrans']), append_lookup_key(models.ForeignKeyModel, 'untrans'))