Update user repository implementation.

repos/user_repo.py

@@ -20,11 +20,13 @@ class UsersRepo:
 
     async def get_user(self, user_id: int):
         user =  await self.collection.find_one({"user_id": user_id})
+        if user:
             user["id"] = str(user["_id"])
         return user
 
     async def get_user_by_username(self, username: str):
         user = await self.collection.find_one({"username": username})
+        if user:
             user["id"] = str(user["_id"])
         return user
 
@@ -48,6 +50,7 @@ class UsersRepo:
         }
         result = await self.collection.insert_one(user_doc)
         user = await self.collection.find_one({"_id": result.inserted_id})
+        if user:
             user["id"] = str(user["_id"])
         return user