Incompatible with latest version of Starlette (v0.18.0)

[TimPansino]

Overview

The newest version of starlette gives a crash when initializing the sub_response on this line.

Specifically, setting status_code=None prevents the Response from initializing due to the code in Starlette's Response.init_headers() on this line.

Stack Trace

.tox/python-framework_strawberry-py39-strawberrylatest/lib/python3.9/site-packages/strawberry/asgi/__init__.py:45: in __call__
    await self.http_handler_class(
.tox/python-framework_strawberry-py39-strawberrylatest/lib/python3.9/site-packages/strawberry/asgi/handlers/http_handler.py:38: in handle
    sub_response = Response(
../../Packages/starlette/starlette/responses.py:50: in __init__
    self.init_headers(headers)

    def init_headers(self, headers: typing.Mapping[str, str] = None) -> None:
        if headers is None:
            raw_headers: typing.List[typing.Tuple[bytes, bytes]] = []
            populate_content_length = True
            populate_content_type = True
        else:
            raw_headers = [
                (k.lower().encode("latin-1"), v.encode("latin-1"))
                for k, v in headers.items()
            ]
            keys = [h[0] for h in raw_headers]
            populate_content_length = b"content-length" not in keys
            populate_content_type = b"content-type" not in keys
    
        body = getattr(self, "body", None)
        if (
            body is not None
            and populate_content_length
>           and not (self.status_code < 200 or self.status_code in (204, 304))
        ):
E       TypeError: '<' not supported between instances of 'NoneType' and 'int'