Allow Optional type annotation

[ScarletBlizzard]

Error when calling Consumer method with return type annotation Optional[...] if response is None:

...
 File "/home/max/.cache/pypoetry/virtualenvs/autom-tnujRd_K-py3.10/lib/python3.10/site-packages/uplink/builder.py", line 100, in __call__
    self._request_definition.define_request(request_builder, args, kwargs)
  File "/home/max/.cache/pypoetry/virtualenvs/autom-tnujRd_K-py3.10/lib/python3.10/site-packages/uplink/commands.py", line 287, in define_request
    self._method_handler.handle_builder(request_builder)
  File "/home/max/.cache/pypoetry/virtualenvs/autom-tnujRd_K-py3.10/lib/python3.10/site-packages/uplink/decorators.py", line 62, in handle_builder
    annotation.modify_request(request_builder)
  File "/home/max/.cache/pypoetry/virtualenvs/autom-tnujRd_K-py3.10/lib/python3.10/site-packages/uplink/returns.py", line 66, in modify_request
    converter = self._get_converter(request_builder, return_type)
  File "/home/max/.cache/pypoetry/virtualenvs/autom-tnujRd_K-py3.10/lib/python3.10/site-packages/uplink/returns.py", line 57, in _get_converter
    return request_builder.get_converter(
  File "/home/max/.cache/pypoetry/virtualenvs/autom-tnujRd_K-py3.10/lib/python3.10/site-packages/uplink/helpers.py", line 96, in get_converter
    return self._converter_registry[converter_key](*args, **kwargs)
  File "/home/max/.cache/pypoetry/virtualenvs/autom-tnujRd_K-py3.10/lib/python3.10/site-packages/uplink/converters/__init__.py", line 52, in __call__
    converter = self._converter_factory(*args, **kwargs)
  File "/home/max/.cache/pypoetry/virtualenvs/autom-tnujRd_K-py3.10/lib/python3.10/site-packages/uplink/converters/__init__.py", line 112, in chain
    converter = func(factory)(*args, **kwargs)
  File "/home/max/.cache/pypoetry/virtualenvs/autom-tnujRd_K-py3.10/lib/python3.10/site-packages/uplink/converters/typing_.py", line 127, in create_response_body_converter
    return self._base_converter(type_)
  File "/home/max/.cache/pypoetry/virtualenvs/autom-tnujRd_K-py3.10/lib/python3.10/site-packages/uplink/converters/typing_.py", line 121, in _base_converter
    if issubclass(type_.__origin__, self.typing.Sequence):
  File "/home/max/.pyenv/versions/3.10.13/lib/python3.10/typing.py", line 1158, in __subclasscheck__
    return issubclass(cls, self.__origin__)
  File "/home/max/.pyenv/versions/3.10.13/lib/python3.10/abc.py", line 123, in __subclasscheck__
    return _abc_subclasscheck(cls, subclass)
TypeError: issubclass() arg 1 must be a class

To Reproduce
Create a Consumer with method that consumes API endpoint that returns None (it is shown as "null" if using curl). Add Optional[SomeType] return type annotation to this method. Call this method to get the error

Expected behavior
Absence of this error. Instead, simply return None

[EvaSDK]

This might not be exactly what you are expecting nor the best solution but for a similar case, in our Harbor API integration, we use the following code to deal with that:

class Success(BaseModel):
    """Placeholder model for successful operations.

    Some operations do not return any data yet `uplink` requires model objects
    to map the response to.
    """


class OptionalJsonStrategy(returns.JsonStrategy):
    """Converts response to object if there is data, else return Success."""

    # pylint: disable=too-few-public-methods

    def __call__(self, response: _ClientResponse) -> BaseModel:  # noqa: D102
        if response.content:
            content = super().__call__(response)
        else:
            content = Success()
        return content


class optional_json(returns.json):  # pylint: disable=invalid-name
    """Specifies that the decorated consumer method should return a JSON object.

    See :class:`uplink.returns.json`.
    """  # noqa: E501

    def _make_strategy(self, converter: Converter) -> OptionalJsonStrategy:
        return OptionalJsonStrategy(converter, self._key)


@optional_json
class HarborAPI(Consumer):
    """These APIs provide services for manipulating Harbor project."""

    @delete(
        "projects/{project_name}/repositories/{repository_name}/"
        "artifacts/{reference}"
    )
    def delete_artifact(
        self,
        project_name: Path,
        repository_name: Path,
        reference: Path,
    ) -> Union[Errors, Success]:
        """Delete the specific artifact."""

Hope it helps.

[EvaSDK]

For reference, here is the excerpt from Harbor spec:
$ jq '.paths["/projects/{project_name_or_id}"].delete' ~/harbor.json

{
  "responses": {
    "200": {
      "$ref": "#/responses/200"
    },
    "404": {
      "$ref": "#/responses/404"
    },
    "403": {
      "$ref": "#/responses/403"
    },
    "412": {
      "$ref": "#/responses/412"
    },
    "400": {
      "$ref": "#/responses/400"
    },
    "500": {
      "$ref": "#/responses/500"
    }
  },
  "parameters": [
    {
      "$ref": "#/parameters/requestId"
    },
    {
      "$ref": "#/parameters/isResourceName"
    },
    {
      "$ref": "#/parameters/projectNameOrId"
    }
  ],
  "tags": [
    "project"
  ],
  "operationId": "deleteProject",
  "summary": "Delete project by projectID",
  "description": "This endpoint is aimed to delete project by project ID."
}

$ jq '.responses["200"]' ~/harbor.json

{
  "headers": {
    "X-Request-Id": {
      "type": "string",
      "description": "The ID of the corresponding request for the response"
    }
  },
  "description": "Success"
}