_getTextboxValueFromOption(option) {
    if (option) {
      return option.choiceValue;
    }
    if (this.modelValue instanceof Unparseable) {
      return this.modelValue.viewValue;
    }
    return this.modelValue;
  }
Return the value to be used for the input value
@overridable
@param {LionOption} option
@returns {string}