toString method
The failure, without the response body.
This used to be prefix + message, where message was the body verbatim.
Since an API is free to echo a rejected request back, and since logging a
caught exception is the most ordinary thing an application does, that put
submitted passwords into crash reports - through the very
catch (err) { log('$err'); } pattern the README recommends. The body is
still available on body for callers that decide they need it.
Implementation
@override
String toString() {
return '$prefix${code ?? (status == null ? 'request failed' : 'HTTP $status')}';
}