Merge pull request #4861 from OctoHuman/master

Fix alert()

lib/renderer/override.js

@@ -157,11 +157,14 @@ window.open = function(url, frameName, features) {
 // Use the dialog API to implement alert().
 window.alert = function(message, title) {
   var buttons;
+  if (arguments.length == 0) {
+    message = '';
+  }
   if (title == null) {
     title = '';
   }
   buttons = ['OK'];
-  message = message.toString();
+  message = String(message);
   remote.dialog.showMessageBox(remote.getCurrentWindow(), {
     message: message,
     title: title,