diff --git a/lib/util.js b/lib/util.js
index 01b0e89..fbd7ab6 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -13,6 +13,7 @@ var util = {
     });
   },
   extend: function(dest, source) {
+    source = source || {}
     for(var key in source) {
       if(source.hasOwnProperty(key)) {
         dest[key] = source[key];