diff --git a/tests/test_filters/test_callback_data.py b/tests/test_filters/test_callback_data.py
index 635b8e9f..7df6b433 100644
--- a/tests/test_filters/test_callback_data.py
+++ b/tests/test_filters/test_callback_data.py
@@ -148,6 +148,13 @@ class TestCallbackData:
         assert MyCallback3.unpack("test3:experiment:42") == MyCallback3(bar=42)
         assert MyCallback3.unpack("test3:spam:42") == MyCallback3(foo="spam", bar=42)
 
+        class MyCallback4(CallbackData, prefix="test4"):
+            foo: Optional[str] = ''
+            bar: Optional[str] = None
+
+        assert MyCallback4.unpack("test4::") == MyCallback4(foo='', bar=None)
+        assert MyCallback4.unpack("test4::") == MyCallback4()
+
     @pytest.mark.parametrize(
         "hint",
         [