static ContentHashBuilder wrap(ContentHashBuilder delegate) {
      return new ContentHashBuilder() {
        boolean hasData = false;
        @Override
        public void update(Object data) {
          hasData = true;
          delegate.update(data);
        }

        @Override
        public Object getResult() {
          return hasData? delegate.getResult() : null;
        }
      };
    }
static ContentHashBuilder wrap(ContentHashBuilder delegate)