getValuesSerialized() {
    let values = {};
    this.fields_.forEach(field => {
      let value = field.serializeValue ? field.serializeValue() : undefined;
      if (value !== undefined) {
        values[field.id_] = field.serializeValue();
      }
    });

    return values;
  }
Returns all available serialized values of the form fields, as an object.
All values in the returned object are either strings or objects.
@type Object