[1.10.x] Refs #26983 -- Added test for isnull lookup to CharField with primary_key=True.

Backport of 97513269d73520d10722bbd10404be6ac4d48d07 from master

2 files changed, 11 insertions, 2 deletions

diff --git a/tests/queries/models.py b/tests/queries/models.py
index 523b58c7e4..c0ce3a5d60 100644
--- a/tests/queries/models.py
+++ b/tests/queries/models.py
@@ -261,7 +261,7 @@ class CustomPk(models.Model):
 
 
 class Related(models.Model):
-    custom = models.ForeignKey(CustomPk, models.CASCADE)
+    custom = models.ForeignKey(CustomPk, models.CASCADE, null=True)
 
 
 class CustomPkTag(models.Model):
diff --git a/tests/queries/tests.py b/tests/queries/tests.py
index a3a810ce5e..46a147c9d8 100644
--- a/tests/queries/tests.py
+++ b/tests/queries/tests.py
@@ -2483,7 +2483,16 @@ class ToFieldTests(TestCase):
             [node1]
         )
 
-    def test_isnull_query(self):
+
+class IsNullTests(TestCase):
+    def test_primary_key(self):
+        custom = CustomPk.objects.create(name='pk')
+        null = Related.objects.create()
+        notnull = Related.objects.create(custom=custom)
+        self.assertSequenceEqual(Related.objects.filter(custom__isnull=False), [notnull])
+        self.assertSequenceEqual(Related.objects.filter(custom__isnull=True), [null])
+
+    def test_to_field(self):
         apple = Food.objects.create(name="apple")
         Eaten.objects.create(food=apple, meal="lunch")
         Eaten.objects.create(meal="lunch")