anchor.diff:    _FixCodeProcessor(this.context, this._migrationCli)
         : pathsToProcess = _migrationCli.computePathsToProcess(context);
   
  -  bool get isPreviewServerRunning => _task?.isPreviewServerRunning ?? false;
  +  bool get isPreviewServerRunning => _task.isPreviewServerRunning;
   
     Future<void> prepareToRerun() async {
       var driver = context.driver;
  
positive.code:         throw _BadArgException(
              'Invalid value for --${CommandLineOptions.previewPortOption}');
        }
        bool? webPreview;
        if (argResults.wasParsed(CommandLineOptions.webPreviewFlag)) {
          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!) {
          throw _BadArgException('--apply-changes requires --no-web-preview');
        }
        var options = CommandLineOptions(
  
negative.code:         _migrationCli.lineInfo[result.path] = result.lineInfo;
        }
        if (_migrationCli.options.ignoreErrors! || analysisErrors.isEmpty) {
          await _task.prepareUnit(result);
        }
      });
  
      var unmigratedDependencies = _task.migration!.unmigratedDependencies;
      if (unmigratedDependencies.isNotEmpty) {
        if (_migrationCli.options.skipImportCheck!) {
          _migrationCli.logger.stdout(unmigratedDependenciesWarning);
  