@protected */
        ready() {
          super.ready();

          const child = this.firstElementChild;
          if (child && child.getAttribute('slot') !== 'filter') {
            console.warn('Make sure you have assigned slot="filter" to the child elements of <vaadin-grid-filter>');
            child.setAttribute('slot', 'filter');
          }
        }

        /** @private */
        _filterChanged(path, value, connected) {
          if (path === undefined || value === undefined || !connected) {
    