anchor.diff:    /// If the request completed, this will be an HTTP status code. If an error
     /// was encountered, this will return 'Error'.
     @override
  -  String get status {
  +  String? get status {
       if (inProgress || !isValid) return null;
  -    String statusCode;
  -    final endArgs = _endEvent.args;
  +    String? statusCode;
  +    final endArgs = _endEvent!.args!;
       if (endArgs.containsKey(HttpRequestData._errorKey)) {
         // This case occurs when an exception has been thrown, so there's no
         // status code to associate with the request.
  
positive.code:   List<HttpInstantEvent> get instantEvents => _instantEvents;
  
    @override
    String get method {
      if (!isValid) return null;
      assert(_startEvent.args.containsKey(HttpRequestData._methodKey));
      return _startEvent.args[HttpRequestData._methodKey];
    }
  
    /// A list of all cookies contained within the request headers.
  
negative.code:     if (status == 'Error') return true;
  
      try {
        final code = int.parse(status!);
        // Status codes 400-499 are client errors and 500-599 are server errors.
        if (code >= 400) {
          return true;
  