Merge pull request #1 from harshithmullapudi/patch-1

Send undefined if the next element doesn't exist

Author: kaushiknishchay

intro.js

@@ -422,7 +422,7 @@
     var continueStep = true;
 
     if (typeof (this._introBeforeChangeCallback) !== 'undefined') {
-      continueStep = this._introBeforeChangeCallback.call(this, nextStep.element);
+      continueStep = this._introBeforeChangeCallback.call(this, nextStep && nextStep.element);
     }
 
     // if `onbeforechange` returned `false`, stop displaying the element
@@ -463,7 +463,7 @@
     var continueStep = true;
 
     if (typeof (this._introBeforeChangeCallback) !== 'undefined') {
-      continueStep = this._introBeforeChangeCallback.call(this, nextStep.element);
+      continueStep = this._introBeforeChangeCallback.call(this, nextStep && nextStep.element);
     }
 
     // if `onbeforechange` returned `false`, stop displaying the element