diff --git a/src/utils/db/models/session.py b/src/utils/db/models/session.py
index e47f85d..f21ee77 100644
--- a/src/utils/db/models/session.py
+++ b/src/utils/db/models/session.py
@@ -1,4 +1,4 @@
-from typing import Annotated, List
+from typing import Annotated, List, Optional
 
 from beanie import Document, Indexed
 from pydantic import BaseModel, Field
@@ -7,9 +7,9 @@ from pydantic_ai.messages import ModelMessage
 
 class SessionBase(BaseModel):
     chat_id: Annotated[int, Indexed(unique=True)]
-    system_prompt_override: str = None
+    system_prompt_override: Optional[str] = None
     history: List[ModelMessage] = Field(default_factory=list)
-    api_key_override: str = None
+    api_key_override: Optional[str] = None
 
 
 class __CommonSessionRepository(SessionBase, Document):