def METHOD_NAME(
    self, cached: Optional[Mapping[str, Any]]
) -> Dict[str, str]:
    if cached is not None:
        if "etag" in cached:
            return {**self._headers, "If-None-Match": cached["etag"]}
        elif "last_modified" in cached:
            return {**self._headers, "If-Modified-Since": cached["last_modified"]}
    return self._headers