[BUG][PYTHON] AttributeError: module 'open_api_client' has no attribute 'Optional[str]'

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• [ x] Have you validated the input using an OpenAPI validator (example)?
• [x ] Have you tested with the latest master to confirm the issue still exists?
• [x ] Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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This seems to be a pretty simple bug,
From generation it looks like its generating Optional[str] when the schema is items as str.
when deserializing the object it fails to find it under a base python type mapping

Suggest a fix

not sure the best method but what i did locally for now.

if klass.startswith('Optional['):
                m = re.match(r'Optional\[(.*)]', klass)
                assert m is not None, "Malformed Optional type definition"
                klass = m.group(1)
                

\api_client.py", line 317, in response_deserialize
    return_data = self.deserialize(response_text, response_type, content_type)
api_client.py", line 415, in deserialize
    return self.__deserialize(data, response_type)
api_client.py", line 433, in __deserialize
    return [self.__deserialize(sub_data, sub_kls)
\api_client.py", line 433, in <listcomp>
    return [self.__deserialize(sub_data, sub_kls)
\api_client.py", line 447, in __deserialize
    klass = getattr(openapi.models, klass)
AttributeError: module 'openapi.models' has no attribute 'Optional[str]'

Start with the generated api_client.py traceback, especially response_deserialize, deserialize, and __deserialize, then locate the OpenAPI Generator template or source that produces this logic. Reproduce the list deserialization case with an Optional[str] item type and add regression coverage showing that deserialization completes without the AttributeError.