Index: wp-includes/nav-menu-template.php
===================================================================
--- wp-includes/nav-menu-template.php	(revision 14414)
+++ wp-includes/nav-menu-template.php	(working copy)
@@ -220,10 +220,14 @@
 		}
 	}
 
+	// If no fallback function was specified and the menu doesn't exists, bail.
+	if ( !$menu || is_wp_error($menu) )
+		return false;
+	
 	$nav_menu = '';
 	$items = '';
 	$container_allowedtags = apply_filters( 'wp_nav_menu_container_allowedtags', array( 'div', 'p', 'nav' ) );
-
+	
 	if ( in_array( $args->container, $container_allowedtags ) ) {
 		$class = $args->container_class ? ' class="' . esc_attr($args->container_class) . '"' : ' class="menu-'. $menu->slug .'-container"';
 		$nav_menu .= '<'. $args->container . $class .'>';