Seralizes and returns the response body.

        On subsequent access, returns the cached value.

def body(self):
        """Seralizes and returns the response body.

        On subsequent access, returns the cached value."""
        if self._body is None:
            raw_body = self._raw_body
            if self._body_writer is None:
                self._body = raw_body() if callable(raw_body) else raw_body
            else:
                self._body = self._body_writer(raw_body)

        return self._body