anchor.diff:  
     /// The response headers for the HTTP request.
     @override
  -  Map<String, dynamic> get responseHeaders {
  +  Map<String, dynamic>? get responseHeaders {
       // The request may still be in progress, in which case we don't display any
       // headers, or the request may be invalid, in which case we also don't
       // display any headers.
       if (inProgress || !isValid) return null;
  -    return _endEvent.args[HttpRequestData._responseHeadersKey];
  +    return _endEvent!.args![HttpRequestData._responseHeadersKey];
     }
   
     /// A string representing the status of the request.
  
positive.code: 
    @override
    DateTime get endTimestamp => DateTime.fromMicrosecondsSinceEpoch(
          timelineMicrosecondsSinceEpoch(_endTime),
        );
  
    @override
  
negative.code:       );
  
    @override
    String? get status =>
        _hasError ? 'Error' : _request.response?.statusCode.toString();
  
    @override
    String get uri => _request.uri.toString();
  
    @override
    String? get responseBody {
      if (_request is! HttpProfileRequest) {
        return null;
      }
  