diff --git a/aiogram/client/bot.py b/aiogram/client/bot.py
index 1c6de27c..ab25a549 100644
--- a/aiogram/client/bot.py
+++ b/aiogram/client/bot.py
@@ -20,9 +20,7 @@ from typing import (
 import aiofiles
 
 from aiogram.utils.token import extract_bot_id, validate_token
-from .default import Default, DefaultBotProperties
-from .session.aiohttp import AiohttpSession
-from .session.base import BaseSession
+
 from ..methods import (
     AddStickerToSet,
     AnswerCallbackQuery,
@@ -235,6 +233,9 @@ from ..types import (
     UserProfilePhotos,
     WebhookInfo,
 )
+from .default import Default, DefaultBotProperties
+from .session.aiohttp import AiohttpSession
+from .session.base import BaseSession
 
 T = TypeVar("T")
 
diff --git a/aiogram/client/form.py b/aiogram/client/form.py
index fb6511df..0e2750da 100644
--- a/aiogram/client/form.py
+++ b/aiogram/client/form.py
@@ -30,7 +30,10 @@ def _extract_files(value: Any) -> Tuple[Any, Dict[str, InputFile]]:
     return value, files
 
 
-def extract_files(model: M, files: Dict[str, InputFile] = None) -> Tuple[M, Dict[str, InputFile]]:
+def extract_files(
+    model: M,
+    files: Optional[Dict[str, InputFile]] = None,
+) -> Tuple[M, Dict[str, InputFile]]:
     if files is None:
         files = {}
     update = {}
@@ -53,7 +56,7 @@ def extract_files(model: M, files: Dict[str, InputFile] = None) -> Tuple[M, Dict
     return modified_model, files
 
 
-def form_serialize(value: Any) -> Optional[str]:
+def form_serialize(value: Any) -> str:
     """
     Prepare jsonable value to send
     """
diff --git a/aiogram/types/base.py b/aiogram/types/base.py
index e251cfa0..6756e3a1 100644
--- a/aiogram/types/base.py
+++ b/aiogram/types/base.py
@@ -1,4 +1,4 @@
-from typing import Any, Dict
+from typing import Any, Dict, Union
 from unittest.mock import sentinel
 
 from pydantic import (
@@ -40,7 +40,9 @@ class TelegramObject(BotContextController, BaseModel):
         return {k: v for k, v in values.items() if not isinstance(v, UNSET_TYPE)}
 
     @model_serializer(mode="wrap", when_used="json")
-    def json_serialize(self, serializer: SerializerFunctionWrapHandler):
+    def json_serialize(
+        self, serializer: SerializerFunctionWrapHandler
+    ) -> Union[Dict[str, Any], Any]:
         """
         Replacing `Default` placeholders with actual values from bot defaults.
         Ensures JSON serialization backward compatibility by handling non-standard objects.
@@ -51,7 +53,7 @@ class TelegramObject(BotContextController, BaseModel):
                 key: properties[value.name] for key, value in self if isinstance(value, Default)
             }
             return serializer(self.model_copy(update=default_fields))
-        return serializer(self)
+        return serializer(self)  # FIXME: why non-TelegramObject passed there?
 
 
 class MutableTelegramObject(TelegramObject):
diff --git a/aiogram/types/custom.py b/aiogram/types/custom.py
index 0fc6ecc8..252bdf75 100644
--- a/aiogram/types/custom.py
+++ b/aiogram/types/custom.py
@@ -1,7 +1,8 @@
 from datetime import datetime, timedelta
-from typing import Annotated, Union
+from typing import Union
 
 from pydantic import PlainSerializer
+from typing_extensions import Annotated
 
 # Make datetime compatible with Telegram Bot API (unixtime)
 
diff --git a/aiogram/types/input_file.py b/aiogram/types/input_file.py
index 692b0fd9..1fefb80e 100644
--- a/aiogram/types/input_file.py
+++ b/aiogram/types/input_file.py
@@ -116,8 +116,8 @@ class FSInputFile(InputFile):
             chunk_size=chunk_size,
         )
 
-    @model_validator(mode="after")
-    def filename_from_path(self):
+    @model_validator(mode="after")  # type: ignore
+    def filename_from_path(self) -> None:
         self.filename = self.filename or Path(self.path).name
 
     async def read(self, bot: "Bot") -> AsyncGenerator[bytes, None]:
@@ -162,6 +162,8 @@ class URLInputFile(BotContextController, InputFile):
 
     async def read(self, bot: Optional["Bot"] = None) -> AsyncGenerator[bytes, None]:
         bot = self.bot or bot  # FIXME: invalid order suspected
+        if bot is None:
+            raise AttributeError("There is no default bot. Specify it through param")
         stream = bot.session.stream_content(
             url=self.url,
             headers=self.headers,