Fix CallbackData without default Optional (#1370)

* fix: CallbackData set optional as None

* docs: add fix changelog

* Add support for nullable fields in callback data

This update extends the callback data handling by adding support for nullable fields. The code now uses the Python typing structures `Optional` and `Union` to parse such fields correctly. A helper function `_check_field_is_nullable` has been added to assist in efficiently checking if a given field is nullable.

* Add support for nullable fields in callback data

This update extends the callback data handling by adding support for nullable fields. The code now uses the Python typing structures `Optional` and `Union` to parse such fields correctly. A helper function `_check_field_is_nullable` has been added to assist in efficiently checking if a given field is nullable.

---------

Co-authored-by: JRoot Junior <jroot.junior@gmail.com>

tests/test_filters/test_callback_data.py

@@ -1,7 +1,7 @@
 from decimal import Decimal
 from enum import Enum, auto
 from fractions import Fraction
-from typing import Optional
+from typing import Optional, Union
 from uuid import UUID
 
 import pytest
@@ -147,6 +147,22 @@ class TestCallbackData:
         assert MyCallback3.unpack("test3:experiment:42") == MyCallback3(bar=42)
         assert MyCallback3.unpack("test3:spam:42") == MyCallback3(foo="spam", bar=42)
 
+    @pytest.mark.parametrize(
+        "hint",
+        [
+            Union[int, None],
+            Optional[int],
+        ],
+    )
+    def test_unpack_optional_wo_default(self, hint):
+        """Test CallbackData without default optional."""
+
+        class TgData(CallbackData, prefix="tg"):
+            chat_id: int
+            thread_id: hint
+
+        assert TgData.unpack("tg:123:") == TgData(chat_id=123, thread_id=None)
+
     def test_build_filter(self):
         filter_object = MyCallback.filter(F.foo == "test")
         assert isinstance(filter_object.rule, MagicFilter)