diff -r 3d4e9c994f10 -r a86126ab1dd4 wp/wp-includes/class-walker-nav-menu.php
--- a/wp/wp-includes/class-walker-nav-menu.php	Tue Oct 22 16:11:46 2019 +0200
+++ b/wp/wp-includes/class-walker-nav-menu.php	Tue Dec 15 13:49:49 2020 +0100
@@ -50,7 +50,7 @@
 	 * @param int      $depth  Depth of menu item. Used for padding.
 	 * @param stdClass $args   An object of wp_nav_menu() arguments.
 	 */
-	public function start_lvl( &$output, $depth = 0, $args = array() ) {
+	public function start_lvl( &$output, $depth = 0, $args = null ) {
 		if ( isset( $args->item_spacing ) && 'discard' === $args->item_spacing ) {
 			$t = '';
 			$n = '';
@@ -89,7 +89,7 @@
 	 * @param int      $depth  Depth of menu item. Used for padding.
 	 * @param stdClass $args   An object of wp_nav_menu() arguments.
 	 */
-	public function end_lvl( &$output, $depth = 0, $args = array() ) {
+	public function end_lvl( &$output, $depth = 0, $args = null ) {
 		if ( isset( $args->item_spacing ) && 'discard' === $args->item_spacing ) {
 			$t = '';
 			$n = '';
@@ -115,7 +115,7 @@
 	 * @param stdClass $args   An object of wp_nav_menu() arguments.
 	 * @param int      $id     Current item ID.
 	 */
-	public function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
+	public function start_el( &$output, $item, $depth = 0, $args = null, $id = 0 ) {
 		if ( isset( $args->item_spacing ) && 'discard' === $args->item_spacing ) {
 			$t = '';
 			$n = '';
@@ -203,7 +203,7 @@
 
 		$attributes = '';
 		foreach ( $atts as $attr => $value ) {
-			if ( ! empty( $value ) ) {
+			if ( is_scalar( $value ) && '' !== $value && false !== $value ) {
 				$value       = ( 'href' === $attr ) ? esc_url( $value ) : esc_attr( $value );
 				$attributes .= ' ' . $attr . '="' . $value . '"';
 			}
@@ -259,7 +259,7 @@
 	 * @param int      $depth  Depth of page. Not Used.
 	 * @param stdClass $args   An object of wp_nav_menu() arguments.
 	 */
-	public function end_el( &$output, $item, $depth = 0, $args = array() ) {
+	public function end_el( &$output, $item, $depth = 0, $args = null ) {
 		if ( isset( $args->item_spacing ) && 'discard' === $args->item_spacing ) {
 			$t = '';
 			$n = '';
@@ -270,4 +270,4 @@
 		$output .= "</li>{$n}";
 	}
 
-} // Walker_Nav_Menu
+}