docs: function (alternativeBackingValue, compare) {
      var value = this.get();
      var alternativeValue = alternativeBackingValue ? alternativeBackingValue.getIn(this._path) : undefined;
      return compare ?
          !compare(value, alternativeValue) :
          !(value === alternativeValue || (Util.undefinedOrNull(value) && Util.undefinedOrNull(alternativeValue)));
    }