refactor: using optional keyword

repositories/deal.py

@@ -1,3 +1,5 @@
+from typing import Optional
+
 from sqlalchemy import select
 
 from models import Deal
@@ -11,7 +13,7 @@ class DealRepository(BaseRepository):
         result = await self.session.execute(stmt)
         return list(result.scalars().all())
 
-    async def get_by_id(self, deal_id: int) -> Deal | None:
+    async def get_by_id(self, deal_id: int) -> Optional[Deal]:
         stmt = select(Deal).where(Deal.id == deal_id, Deal.is_deleted.is_(False))
         result = await self.session.execute(stmt)
         return result.scalar_one_or_none()