public function widget( $args, $instance ) {
    // Get menu.
    $nav_menu = ! empty( $instance['nav_menu'] ) ? wp_get_nav_menu_object( $instance['nav_menu'] ) : false;

    if ( ! $nav_menu ) {
      return;
    }

    $title = ! empty( $instance['title'] ) ? $instance['title'] : '';

    
/** This filter is documented in wp-includes/widgets/class-wp-widget-pages.php */
    $title = apply_filters( 'widget_title', $title, $instance, $this->id_base );

    echo $args['before_widget'];

    if ( $title ) {
      echo $args['before_title'] . $title . $args['after_title'];
    }

    $nav_menu_args = array(
      'fallback_cb' => '',
      'menu'        => $nav_menu,
    );

    
/**
 * Filters the arguments for the Navigation Menu widget.
 *
 * @since 4.2.0
 * @since 4.4.0 Added the `$instance` parameter.
 *
 * @param array    $nav_menu_args {
 *     An array of arguments passed to wp_nav_menu() to retrieve a navigation menu.
 *
 *     @type callable|bool $fallback_cb Callback to fire if the menu doesn't exist. Default empty.
 *     @type mixed         $menu        Menu ID, slug, or name.
 * }
 * @param WP_Term  $nav_menu      Nav menu object for the current menu.
 * @param array    $args          Display arguments for the current widget.
 * @param array    $instance      Array of settings for the current widget.
 */
    wp_nav_menu( apply_filters( 'widget_nav_menu_args', $nav_menu_args, $nav_menu, $args, $instance ) );

    echo $args['after_widget'];
  }