Ticket #32781: 32781.3.diff

src/wp-includes/class-wp-customize-nav-menus.php

@@ -753 +753 @@
                 $args['instance_number'] = $this->preview_nav_menu_instance_number;
 
                 $can_partial_refresh = (
-                        $args['echo']
+                        ! empty( $args['echo'] )
                         &&
-                        is_string( $args['fallback_cb'] )
+                        ( empty( $args['fallback_cb'] ) || is_string( $args['fallback_cb'] ) )
                         &&
-                        is_string( $args['walker'] )
+                        ( empty( $args['walker'] ) || is_string( $args['walker'] ) )
                 );
                 $args['can_partial_refresh'] = $can_partial_refresh;
 
                 if ( ! $can_partial_refresh ) {
-                        unset( $args['fallback_cb'] );
-                        unset( $args['walker'] );
+                        $args['fallback_cb'] = '';
+                        $args['walker'] = '';
                 }
 
                 ksort( $args );

src/wp-includes/nav-menu-template.php

@@ -308 +308 @@
          *  - Otherwise, bail.
          */
         if ( ( !$menu || is_wp_error($menu) || ( isset($menu_items) && empty($menu_items) && !$args->theme_location ) )
-                && $args->fallback_cb && is_callable( $args->fallback_cb ) )
+                && isset( $args->fallback_cb ) && $args->fallback_cb && is_callable( $args->fallback_cb ) )
                         return call_user_func( $args->fallback_cb, (array) $args );
 
         if ( ! $menu || is_wp_error( $menu ) )