anchor.diff:  
       await processResources((ResolvedUnitResult result) async {
         _progressBar.tick();
  -      await _task!.processUnit(result);
  +      await _task.processUnit(result);
       });
       await processResources((ResolvedUnitResult result) async {
         _progressBar.tick();
         if (_migrationCli.shouldBeMigrated(result.path)) {
  -        await _task!.finalizeUnit(result);
  +        await _task.finalizeUnit(result);
         }
       });
       _progressBar.complete();
       _migrationCli.logger.stdout(_migrationCli.ansi
           .emphasized('Compiling instrumentation information...'));
       // Update the tasks paths-to-process, in case of new or deleted files.
  -    _task!.pathsToProcess = pathsToProcess;
  -    var state = await _task!.finish();
  -    _task!.processPackage(context.contextRoot.root, state.neededPackages);
  +    _task.pathsToProcess = pathsToProcess;
  +    var state = await _task.finish();
  +    _task.processPackage(context.contextRoot.root, state.neededPackages);
       if (_migrationCli.options.webPreview!) {
  -      await _task!.startPreviewServer(state, _migrationCli.applyHook);
  -    }
  -    state.previewUrls = _task!.previewUrls;
  +      await _task.startPreviewServer(state, _migrationCli.applyHook);
  +    }
  +    state.previewUrls = _task.previewUrls;
   
       return state;
     }
  
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);
  