anchor.diff:  
     Future removeTag(String uuid) {
       final completer = new Completer();
  +
  +    // validate uuid
  +    if (!PinUtility.isUuid(uuid)) {
  +      PinLogger.instance.shout('[CartModel] removeTag: uuid format invalid: ${uuid}}');
  +      completer.complete(null);
  +    }
   
       tags.remove(uuid, posts);
   
  
positive.code:   }
  
    Future removePost(String uuid) {
  
    }
  
    Future _addPost(String uuid, String markdown, CartPostHeader header, String html) {
  
negative.code:   Future removeCategory(String uuid) {
      final completer = new Completer();
  
      // validate uuid
      if (!PinUtility.isUuid(uuid)) {
        PinLogger.instance.shout('[CartModel] removeCategory: uuid format invalid: ${uuid}}');
        completer.complete(null);
      }
  
      CartCategory category = categories.find(uuid);
      if (category == null) {
        PinLogger.instance.warning('[CartModel] removeCategory: Category not found, uuid: ${uuid}');
  