anchor.diff:      })
       .then((_) {
         if (_ == null) {
  -        return new Future.value(''); // post not exists, '' markdown return
  +        return new Future.value(''); // post not exists, '' return
         } else {
           if (_ == false) { // post exists, markdown file not exists, error
             throw new Exception('[CartAction] handlePostMarkdownFetch: Target markdown file of the post not found: ${uuid}');
  
positive.code:     if (!CartSystem.instance.actionPreProcess(ctx)) {
        return;
      }
      if (!_filterIsMaster(ctx)) {
        return;
      }
  
      String uuid;
      File mdFile;
  
      HttpBodyHandler.processRequest(ctx.req)
  
negative.code:       if (!PinUtility.isUuid(uuid)) {
          throw new Exception('[CartAction] handlePostMarkdownFetch: Invalid post uuid: ${uuid}');
        }
        post = CartModel.instance.postList.find(uuid);
        if (post == null) {
          return new Future.value(null); // post not exists, null return
        } else {
  