[1.10.x] Fixed #26983 -- Fixed isnull filtering on ForeignKey with to_field

Thanks weidwonder for the report.
Backport of 272eccf7ff0ced609e5a5e3bb6b4a40e773e0e66 from master.

1 files changed, 13 insertions, 0 deletions

diff --git a/tests/queries/tests.py b/tests/queries/tests.py
index 48b57376f9..a3a810ce5e 100644
--- a/tests/queries/tests.py
+++ b/tests/queries/tests.py
@@ -2483,6 +2483,19 @@ class ToFieldTests(TestCase):
             [node1]
         )
 
+    def test_isnull_query(self):
+        apple = Food.objects.create(name="apple")
+        Eaten.objects.create(food=apple, meal="lunch")
+        Eaten.objects.create(meal="lunch")
+        self.assertQuerysetEqual(
+            Eaten.objects.filter(food__isnull=False),
+            ['<Eaten: apple at lunch>']
+        )
+        self.assertQuerysetEqual(
+            Eaten.objects.filter(food__isnull=True),
+            ['<Eaten: None at lunch>']
+        )
+
 
 class ConditionalTests(BaseQuerysetTest):
     """Tests whose execution depend on different environment conditions like