Index: wp-includes/nav-menu.php
===================================================================
--- wp-includes/nav-menu.php	(revision 13544)
+++ wp-includes/nav-menu.php	(working copy)
@@ -29,14 +29,17 @@
  * @param int|string $menu The menu to check
  * @return mixed Menu Object, if exists.
  */
-function is_nav_menu( $menu ) {
-	if ( $menu ) {
-		$menu = get_term( $menu, 'nav_menu' );
-	} elseif ( !$menu ) {
-		$menu = get_term_by( 'slug', $menu, 'nav_menu' );
-	} elseif( !$menu ) {
-		$menu = get_term_by( 'name', $menu, 'nav_menu' );
-	} else {
+function is_nav_menu( $value ) {
+	if ( $value ) {
+		$menu = get_term( $value, 'nav_menu' );
+	}
+	if ( !$menu ) {
+		$menu = get_term_by( 'slug', $value, 'nav_menu' );
+	}
+	if ( !$menu ) {
+		$menu = get_term_by( 'name', $value, 'nav_menu' );
+	}
+	if ( !$menu ) {
 		$menu = false;
 	}