fix: mypy errors

aws_lambda_powertools/utilities/idempotency/idempotency.py

@@ -4,6 +4,7 @@
 import functools
 import logging
 import os
+from inspect import isclass
 from typing import Any, Callable, Dict, Optional, Type, Union, cast
 
 from aws_lambda_powertools.middleware_factory import lambda_handler_decorator
@@ -137,7 +138,7 @@ def process_order(customer_id: str, order: dict, **kwargs):
             ),
         )
 
-    if issubclass(output_serializer, BaseIdempotencyModelSerializer):
+    if isclass(output_serializer) and issubclass(output_serializer, BaseIdempotencyModelSerializer):
         # instantiate an instance of the serializer class
         output_serializer = output_serializer.instantiate(function.__annotations__.get("return", None))