Ticket #32816: 32816.diff

class-wp-customize-nav-menu-item-setting.php

@@ -723 +723 @@
                 $menu_item_value['description'] = wp_unslash( apply_filters( 'content_save_pre', wp_slash( $menu_item_value['description'] ) ) );
 
                 $menu_item_value['url'] = esc_url_raw( $menu_item_value['url'] );
+                if( '' === $menu_item_value['url'] ) {
+                        return new WP_Error( 'invalid_url', __( 'Invalid URL.' ) );
+                }
                 if ( 'publish' !== $menu_item_value['status'] ) {
                         $menu_item_value['status'] = 'draft';
                 }