WordPress Overriding default navigation widget to use walker

overriding-navigation-widget.php

<?php

/*
Example 1 - overriding default navigation widget to use walker
Author: Bartek Makowski
*/

//inside wp-content/themes/{template}/functions.php

class LMU_WP_Nav_Menu_Widget extends WP_Nav_Menu_Widget{
    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;

		/** This filter is documented in wp-includes/default-widgets.php */
		$instance['title'] = apply_filters( 'widget_title', empty( $instance['title'] ) ? '' : $instance['title'], $instance, $this->id_base );

		echo $args['before_widget'];

		if ( !empty($instance['title']) )
			echo $args['before_title'] . $instance['title'] . $args['after_title'];

		$nav_menu_args = array(
			'fallback_cb' => '',
			'menu'        => $nav_menu,
                        'container' => 'ul',
                        'echo' => true,
                        'items_wrap' => widget_nav_wrap(),
                        'walker' => new walker_widget_nav()
		);

		/**
		 * Filter the arguments for the Custom Menu widget.
		 *
		 * @since 4.2.0
		 *
		 * @param array    $nav_menu_args {
		 *     An array of arguments passed to wp_nav_menu() to retrieve a custom menu.
		 *
		 *     @type callback|bool $fallback_cb Callback to fire if the menu doesn't exist. Default empty.
		 *     @type mixed         $menu        Menu ID, slug, or name.
		 * }
		 * @param stdClass $nav_menu      Nav menu object for the current menu.
		 * @param array    $args          Display arguments for the current widget.
		 */
		wp_nav_menu( apply_filters( 'widget_nav_menu_args', $nav_menu_args, $nav_menu, $args ) );

		echo $args['after_widget'];
	}
}

function myplugin_register_widgets() {
	register_widget( 'LMU_WP_Nav_Menu_Widget' );
}

add_action( 'widgets_init', 'myplugin_register_widgets' );