1 files changed, 14 insertions, 0 deletions
diff --git a/tests/backends/postgresql/tests.py b/tests/backends/postgresql/tests.py
index 31aac022c8..a045195991 100644
--- a/tests/backends/postgresql/tests.py
+++ b/tests/backends/postgresql/tests.py
@@ -369,6 +369,20 @@ class Tests(TestCase):
             with self.subTest(lookup=lookup):
                 self.assertIn("::text", do.lookup_cast(lookup))
 
+    def test_lookup_cast_isnull_noop(self):
+        from django.db.backends.postgresql.operations import DatabaseOperations
+
+        do = DatabaseOperations(connection=None)
+        # Using __isnull lookup doesn't require casting.
+        tests = [
+            "CharField",
+            "EmailField",
+            "TextField",
+        ]
+        for field_type in tests:
+            with self.subTest(field_type=field_type):
+                self.assertEqual(do.lookup_cast("isnull", field_type), "%s")
+
     def test_correct_extraction_psycopg_version(self):
         from django.db.backends.postgresql.base import Database, psycopg_version