diff --git a/lib/XMLHttpRequest.js b/lib/XMLHttpRequest.js
index 949fdf9..2fdbb28 100644
--- a/lib/XMLHttpRequest.js
+++ b/lib/XMLHttpRequest.js
@@ -284,6 +284,7 @@ exports.XMLHttpRequest = function() {
         break;
 
       case undefined:
+      case null:
       case "":
         host = "localhost";
         break;