Calling exit() on null issue solved

Author: puneetkay

intro.js

@@ -278,6 +278,10 @@
   function _exitIntro(targetElement) {
     //remove overlay layer from the page
     var overlayLayer = targetElement.querySelector('.introjs-overlay');
+    //return if intro already completed or skipped
+    if(overlayLayer == null){
+      return;
+    }
     //for fade-out animation
     overlayLayer.style.opacity = 0;
     setTimeout(function () {