diff --git a/tests/grids/test_base.py b/tests/grids/test_base.py
index d5f3766..1002ac9 100644
--- a/tests/grids/test_base.py
+++ b/tests/grids/test_base.py
@@ -1433,7 +1433,7 @@ class TestGrid(WebTestCase):
         # null
         obj = MagicMock(dt=None)
         result = grid.render_date(obj, 'dt', None)
-        self.assertIsNone(result)
+        self.assertEqual(result, '')
 
         # typical
         dt = datetime.date(2025, 1, 13)
@@ -1446,7 +1446,7 @@ class TestGrid(WebTestCase):
 
         obj = MagicMock(dt=None)
         result = grid.render_datetime(obj, 'dt', None)
-        self.assertIsNone(result)
+        self.assertEqual(result, '')
 
         dt = datetime.datetime(2024, 12, 12, 13, 44, tzinfo=datetime.timezone.utc)
         obj = MagicMock(dt=dt)