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.

aiogram/filters/callback_data.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import typing
 from decimal import Decimal
 from enum import Enum
 from fractions import Fraction
@@ -18,6 +19,7 @@ from uuid import UUID
 
 from magic_filter import MagicFilter
 from pydantic import BaseModel
+from pydantic.fields import FieldInfo
 
 from aiogram.filters.base import Filter
 from aiogram.types import CallbackQuery
@@ -120,8 +122,9 @@ class CallbackData(BaseModel):
             raise ValueError(f"Bad prefix ({prefix!r} != {cls.__prefix__!r})")
         payload = {}
         for k, v in zip(names, parts):  # type: str, Optional[str]
-            if v == "":
-                v = None
+            if field := cls.model_fields.get(k):
+                if v == "" and _check_field_is_nullable(field):
+                    v = None
             payload[k] = v
         return cls(**payload)
 
@@ -179,3 +182,19 @@ class CallbackQueryFilter(Filter):
         if self.rule is None or self.rule.resolve(callback_data):
             return {"callback_data": callback_data}
         return False
+
+
+def _check_field_is_nullable(field: FieldInfo) -> bool:
+    """
+    Check if the given field is nullable.
+
+    :param field: The FieldInfo object representing the field to check.
+    :return: True if the field is nullable, False otherwise.
+
+    """
+    if not field.is_required():
+        return True
+
+    return typing.get_origin(field.annotation) is typing.Union and type(None) in typing.get_args(
+        field.annotation
+    )

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
@@ -147,12 +147,19 @@ class TestCallbackData:
         assert MyCallback3.unpack("test3:experiment:42") == MyCallback3(bar=42)
         assert MyCallback3.unpack("test3:spam:42") == MyCallback3(foo="spam", bar=42)
 
-    def test_unpack_optional_wo_default(self):
+    @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: Optional[int]
+            thread_id: hint
 
         assert TgData.unpack("tg:123:") == TgData(chat_id=123, thread_id=None)