Update user repository implementation.

repos/user_repo.py

@@ -20,12 +20,14 @@ class UsersRepo:
 
     async def get_user(self, user_id: int):
         user =  await self.collection.find_one({"user_id": user_id})
-        user["id"] = str(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})
-        user["id"] = str(user["_id"])
+        if user:
+            user["id"] = str(user["_id"])
         return user
 
     async def create_user(self, username: str, password: str, full_name: Optional[str] = None):
@@ -48,7 +50,8 @@ class UsersRepo:
         }
         result = await self.collection.insert_one(user_doc)
         user = await self.collection.find_one({"_id": result.inserted_id})
-        user["id"] = str(user["_id"])
+        if user:
+            user["id"] = str(user["_id"])
         return user
 
     async def get_pending_users(self):