content_type_value = request.headers.get("content-type")
                            if not content_type_value:
                                json_body = await request.json()
                            else:
                                message = email.message.Message()
                                message["content-type"] = content_type_value

        ] = None,
        lifespan: Annotated[
            Optional[Lifespan[AppType]],
            Doc(
                """
                A `Lifespan` context manager handler. This replaces `startup` and
                `shutdown` functions with a single context manager.

                Read more in the
                [FastAPI docs for `lifespan`](https://fastapi.tiangolo.com/advanced/events/).
                """