Merge branch 'CB-7444' of https://github.com/MSOpenTech/cordova-wp8
diff --git a/wp8/template/cordovalib/XHRHelper.cs b/wp8/template/cordovalib/XHRHelper.cs
index fa7b617..81256fe 100644
--- a/wp8/template/cordovalib/XHRHelper.cs
+++ b/wp8/template/cordovalib/XHRHelper.cs
@@ -316,7 +316,7 @@
                     if (resource == null)
                     {
                         // 404 ?
-                        Browser.InvokeScript("__onXHRLocalCallback", new string[] { "404", null, reqId });
+                        Browser.InvokeScript("__onXHRLocalCallback", new string[] { "404", string.Empty, reqId });
                         return true;
                     }
                     else