Ticket #13437: 13437.patch

wp-includes/link-template.php

@@ -1963 +1963 @@
         if ( !empty($path) && is_string($path) && strpos($path, '..') === false )
                 $url .= ltrim($path, '/');
 
-        return apply_filters('admin_url', $url, $path, $blog_id);
+        return (string) apply_filters('admin_url', $url, $path, $blog_id);
 }
 
 /**