anchor.diff:    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}');
  
positive.code:   Future addCategory(String uuid, String name) {
      final completer = new Completer();
  
      var timestamp = PinTime.getTime();
  
      categories.addNewCategory(uuid, name, timestamp: timestamp);
  
negative.code:   Future addTag(String uuid, String name) {
      final completer = new Completer();
  
      // validate uuid
      if (!PinUtility.isUuid(uuid)) {
        PinLogger.instance.shout('[CartModel] addTag: uuid format invalid: ${uuid}}');
        completer.complete(null);
      }
  
      int timestamp = PinTime.getTime();
  
      tags.addNewTag(uuid, name, timestamp: timestamp);
  