René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Invalid Code is generated for lists inside a union","articleBody":"**Describe the bug**\r\nWhen a list occurs inside a union, [this call](https://github.com/openapi-generators/openapi-python-client/blob/508a841eea69da5f8e868ee20d785b16426212d4/openapi_python_client/templates/property_templates/union_property.py.jinja#L31) causes the list template to initialize the value with `UNSET` instead of `[]`. The list template then tries to call `append` on `UNSET`, which of course does not work.\r\n\r\n**OpenAPI Spec File**\r\n[A link to your openapi.json which produces this issue.](https://gist.github.com/diesieben07/267dd33e21a206ce4bc9a8906bba259e)\r\n\r\n**Desktop (please complete the following information):**\r\n - OS: Ubuntu 22.04.2\r\n - Python Version: 2.10.8\r\n - openapi-python-client version 0.14.0\r\n\r\n**Additional context**\r\nThe above OpneAPI spec file generates the following code, for reference:\r\n```python\r\ndef _parse_response(\r\n    *, client: Client, response: httpx.Response\r\n) -\u003e Optional[Union[\"GetExampleResponse200Type0\", List[\"GetExampleResponse200Type1Item\"]]]:\r\n    if response.status_code == HTTPStatus.OK:\r\n\r\n        def _parse_response_200(\r\n            data: object,\r\n        ) -\u003e Union[\"GetExampleResponse200Type0\", List[\"GetExampleResponse200Type1Item\"]]:\r\n            try:\r\n                if not isinstance(data, dict):\r\n                    raise TypeError()\r\n                response_200_type_0 = GetExampleResponse200Type0.from_dict(data)\r\n\r\n                return response_200_type_0\r\n            except:  # noqa: E722\r\n                pass\r\n            if not isinstance(data, list):\r\n                raise TypeError()\r\n            response_200_type_1 = UNSET # PROBLEM IS HERE\r\n            _response_200_type_1 = data\r\n            for response_200_type_1_item_data in _response_200_type_1:\r\n                response_200_type_1_item = GetExampleResponse200Type1Item.from_dict(response_200_type_1_item_data)\r\n\r\n                response_200_type_1.append(response_200_type_1_item)\r\n\r\n            return response_200_type_1\r\n\r\n        response_200 = _parse_response_200(response.json())\r\n\r\n        return response_200\r\n    if client.raise_on_unexpected_status:\r\n        raise errors.UnexpectedStatus(response.status_code, response.content)\r\n    else:\r\n        return None\r\n```\r\n","author":{"url":"https://github.com/diesieben07","@type":"Person","name":"diesieben07"},"datePublished":"2023-05-04T12:02:59.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/756/openapi-python-client/issues/756"}