anchor.diff:    }
   }
   
  -class ShipFilter {
  +class ShipFilter extends Observable {
     ShipFilter.fromJSON(Map<String, dynamic> data) {
     }
   
  
positive.code:       ship.belongingFleet = null;
      }
    }
  }
negative.code:   }
  }
  
  class ShipPredicate extends Observable {
    @observable final List<ShipPredicate> or =
        new ObservableList<ShipPredicate>();
    @observable final List<ShipPredicate> and =
  