diff --git a/src/url/index.js b/src/url/index.js
index c4963b93..5cfecd26 100644
--- a/src/url/index.js
+++ b/src/url/index.js
@@ -60,6 +60,10 @@ Url.params = function (obj) {
     var params = [], escape = encodeURIComponent;
 
     params.add = function (key, value) {
+        
+        if (value === undefined) {
+            return;
+        }
 
         if (isFunction(value)) {
             value = value();