From 658f1fc082e2d2ae485537a5b752d53bc1554483 Mon Sep 17 00:00:00 2001
From: m-xim <170838360+m-xim@users.noreply.github.com>
Date: Tue, 11 Mar 2025 01:14:13 +0300
Subject: [PATCH] Fix handling of default empty string ("") in CallbackData
 filter (#1493)

* Update callback_data.py

Allows using a default value in the class which is equal to an empty string ("").

Example:
class MyCallbackData(CallbackData, prefix="MyCallbackData"):
    input1: str
    input2: str = ""

* Create 1493.bugfix.rst

* Update callback_data.py

Fixed an issue that prevented unpacking None values.

* Added tests for CallbackData

* Update tests/test_filters/test_callback_data.py

Co-authored-by: Oleg A. <t0rr@mail.ru>

* Update test_callback_data.py

* Update callback_data.py

* Update 1493.bugfix.rst

---------

Co-authored-by: Oleg A. <t0rr@mail.ru>
---
 CHANGES/1493.bugfix.rst                  | 1 +
 aiogram/filters/callback_data.py         | 5 +++--
 tests/test_filters/test_callback_data.py | 7 +++++++
 3 files changed, 11 insertions(+), 2 deletions(-)
 create mode 100644 CHANGES/1493.bugfix.rst

diff --git a/CHANGES/1493.bugfix.rst b/CHANGES/1493.bugfix.rst
new file mode 100644
index 00000000..386cdb71
--- /dev/null
+++ b/CHANGES/1493.bugfix.rst
@@ -0,0 +1 @@
+Fix handling of default empty string ("") in CallbackData filter
diff --git a/aiogram/filters/callback_data.py b/aiogram/filters/callback_data.py
index c60cd818..e504d50b 100644
--- a/aiogram/filters/callback_data.py
+++ b/aiogram/filters/callback_data.py
@@ -22,6 +22,7 @@ from uuid import UUID
 from magic_filter import MagicFilter
 from pydantic import BaseModel
 from pydantic.fields import FieldInfo
+from pydantic_core import PydanticUndefined
 
 from aiogram.filters.base import Filter
 from aiogram.types import CallbackQuery
@@ -130,8 +131,8 @@ class CallbackData(BaseModel):
         payload = {}
         for k, v in zip(names, parts):  # type: str, Optional[str]
             if field := cls.model_fields.get(k):
-                if v == "" and _check_field_is_nullable(field):
-                    v = None
+                if v == "" and _check_field_is_nullable(field) and field.default != "":
+                    v = field.default if field.default is not PydanticUndefined else None
             payload[k] = v
         return cls(**payload)
 
diff --git a/tests/test_filters/test_callback_data.py b/tests/test_filters/test_callback_data.py
index 8cc2f51f..1bc50cae 100644
--- a/tests/test_filters/test_callback_data.py
+++ b/tests/test_filters/test_callback_data.py
@@ -160,6 +160,13 @@ 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",
         [