Index: wp-includes/post.php
===================================================================
--- wp-includes/post.php	(revision 12570)
+++ wp-includes/post.php	(working copy)
@@ -2401,7 +2401,7 @@
 function &get_page_hierarchy( &$pages, $page_id = 0 ) {
 
 	if ( empty( $pages ) ) {
-		$result = null;
+		$result = array();
 		return $result;
 	}