anchor.diff:          throw _BadArgException(
               'Invalid value for --${CommandLineOptions.previewPortOption}');
         }
  -      bool? webPreview;
  +      bool webPreview;
         if (argResults.wasParsed(CommandLineOptions.webPreviewFlag)) {
  -        webPreview = argResults[CommandLineOptions.webPreviewFlag] as bool?;
  +        webPreview = argResults[CommandLineOptions.webPreviewFlag] as bool;
         } else {
           // If the `webPreviewFlag` wasn't explicitly passed, then the value of
           // this option is based on the value of the [applyChanges] option.
           webPreview = !applyChanges;
         }
  -      if (applyChanges && webPreview!) {
  +      if (applyChanges && webPreview) {
           throw _BadArgException('--apply-changes requires --no-web-preview');
         }
         var options = CommandLineOptions(
  
positive.code:     if (analysisResult.hasErrors && !options.ignoreErrors!) {
        _logErrors(analysisResult);
        return MigrationState(
            _fixCodeProcessor!._task!.migration,
            _fixCodeProcessor!._task!.includedRoot,
            _dartFixListener,
            _fixCodeProcessor!._task!.instrumentationListener,
            {},
            _fixCodeProcessor!._task!.shouldBeMigratedFunction,
            analysisResult);
      } else if (analysisResult.allSourcesAlreadyMigrated) {
        _logAlreadyMigrated();
        return MigrationState(
            _fixCodeProcessor!._task!.migration,
            _fixCodeProcessor!._task!.includedRoot,
            _dartFixListener,
            _fixCodeProcessor!._task!.instrumentationListener,
            {},
            _fixCodeProcessor!._task!.shouldBeMigratedFunction,
            analysisResult);
      } else {
        logger.stdout(ansi.emphasized('Re-generating migration suggestions...'));
  
negative.code:           summary: argResults[CommandLineOptions.summaryOption] as String?,
            webPreview: webPreview);
        return MigrationCliRunner(this, options,
            logger: isVerbose ? loggerFactory(true) : null);
      } on Object catch (exception) {
        handleArgParsingException(exception);
        return null;
  