anchor.diff:      CartTag tag = tagList.addNewTag(uuid, name, timestamp: timestamp);
   
       tagList.dump()
  -    .then((_) {
  -      completer.complete(tag);
  -    })
  +    .then((_) => completer.complete(tag))
       .catchError((e, trace) {
         PinUtility.handleError(e, trace);
         completer.completeError(e, trace);
  
positive.code:       post = _;
        return _postUpload(post, markdown);
      })
      .then((CartPost _) {
        return saveDatabase();
      })
      .then((_) {
        completer.complete(post.generateHeaderInfo());
      })
      .catchError((e, trace) {
        PinUtility.handleError(e, trace);
        completer.completeError(e, trace);
  
negative.code:         return new Future.value(files.items.removeAt(0)); // shall only contains 1 item
        }
      })
      .then((GoogleDriveClient.File file) => completer.complete(file.id))
      .catchError((e, trace) {
        PinUtility.handleError(e, trace);
        completer.completeError(e, trace);
  