Getting error Unsupported value: <FlutterError: 0x60c000225500> of type FlutterError

Do you know what that error means?

Here is the code I added. Same happens with full screen WebViewScaffold.

flutterWebviewPlugin.launch("http://www.cnn.com",
rect: new Rect.fromLTWH(
0.0, 0.0, MediaQuery.of(context).size.width, 300.0),
userAgent: kAndroidUserAgent);