anchor.diff:  
       docHandler = DocHandler(editor, _context);
   
  -    dartServices.version().then((VersionResponse version) {
  -      // "Based on Flutter 1.19.0-4.1.pre Dart SDK 2.8.4"
  -      var versionText = 'Based on Flutter ${version.flutterVersion}'
  -          ' Dart SDK ${version.sdkVersionFull}';
  -      querySelector('#dartpad-version').text = versionText;
  -    }).catchError((e) => null);
  +    updateVersion();
   
       analysisResultsController = AnalysisResultsController(
           DElement(querySelector('#issues')),
  
positive.code: 
    void _handleNullSafetySwitched(bool enabled) {
      var api = deps[DartservicesApi] as DartservicesApi;
      if (enabled) {
        api.rootUrl = nullSafetyServerUrl;
        window.localStorage['null_safety'] = 'true';
  
negative.code:       api.rootUrl = serverUrl;
        window.localStorage['null_safety'] = 'false';
      }
  
      updateVersion();
  
      QueryParams.nullSafety = enabled;
  
  