message: response body into error
diff: @@ -141,4 +141,11 @@ impl ResponseBody {
  _ => None,
  }
  }
  +
  + pub fn into_error(self) -> Option<ErrorBody> {
  + match self {
  + ResponseBody::Error(err) => Some(err),
  + _ => None,
  + }
  + }
  }
  