build method Null safety

Implementation

@override
Widget build(BuildContext context) {
  final AppLocalizations appLocalizations = AppLocalizations.of(context);

  return Container(
    decoration: BoxDecoration(
      color: Theme.of(context).colorScheme.surface,
      borderRadius: ROUNDED_BORDER_RADIUS,
    ),
    child: Column(
      mainAxisSize: MainAxisSize.max,
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Row(
          mainAxisSize: MainAxisSize.max,
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(barcode, style: Theme.of(context).textTheme.subtitle1),
          ],
        ),
        const SizedBox(
          height: 12.0,
        ),
        ProductDialogHelper.getErrorMessage(
          appLocalizations.product_internet_error,
        ),
        const SizedBox(
          height: 12.0,
        ),
        ElevatedButton(
          onPressed: () async {
            await context
                .read<ContinuousScanModel>()
                .retryBarcodeFetch(barcode);
          },
          child: Text(appLocalizations.retry_button_label),
        ),
      ],
    ),
  );
}