build method Null safety

Implementation

@override
Widget build(BuildContext context) {
  final List<String> fullFilenames = getCachedFilenames();
  if (fullFilenames.isEmpty) {
    return getDefaultUnknown();
  }
  return Image.network(
    iconUrl!,
    width: width,
    height: height,
    fit: BoxFit.contain,
    loadingBuilder: (
      final BuildContext context,
      final Widget child,
      final ImageChunkEvent? loadingProgress,
    ) {
      if (loadingProgress == null) {
        return child;
      }
      return displayAssetWhileWaiting
          ? RasterAsyncAsset(
              AssetCacheHelper(
                fullFilenames,
                iconUrl!,
                width: width,
                height: height,
              ),
            )
          : getCircularProgressIndicator();
    },
  );
}