cords the previous value,
       * and adds it to the set of "pending changes" that will be passed to the
       * `_propertiesChanged` callback.  This method does not enqueue the
       * `_propertiesChanged` callback.
       *
       * @param {string} property Name of the property
       * @param {*} value Value to set
       * @return {boolean} Returns true if the property changed
       * @protected
       */
      _setPendingProperty(property, value) {
        let old = this.__data[property];
        i