Index: src/wp-includes/nav-menu-template.php
===================================================================
--- src/wp-includes/nav-menu-template.php	(revision 25717)
+++ src/wp-includes/nav-menu-template.php	(working copy)
@@ -317,7 +317,7 @@
 	 */
 	$sorted_menu_items = apply_filters( 'wp_nav_menu_objects', $sorted_menu_items, $args );
 
-	$items .= walk_nav_menu_tree( $sorted_menu_items, $args->depth, $args );
+	$items .= walk_nav_menu_tree( $sorted_menu_items, $args->depth, (array) $args );
 	unset($sorted_menu_items);
 
 	// Attributes