anchor.diff:    }
   
     @override
  -  Future invalidate(DragonKey key) {
  +  Future<Null> invalidate(DragonKey key) {
       return new File(_pathForKey(key)).delete();
     }
   }
  
positive.code:       pathPackage.join(cacheDir, key.toDragonPath());
  
    @override
    Future<String> get(DragonKey key, {Loader<DragonKey> ifAbsent}) async {
      File file = new File(_pathForKey(key));
      if (await file.exists()) {
        _log.info('Cache hit: $key');
  
negative.code:   }
  
    @override
    Future<Null> set(DragonKey key, String value) async {
      _log.info('Cache set: $key ${value.length} bytes.');
      File file = new File(_pathForKey(key));
      file = await file.create(recursive: true);
  