Merge pull request #1992 from Truimo/dev

fix for #1940: check if there is no parent element

tracker/index.js

@@ -119,6 +119,9 @@
             return currentElement;
           }
           currentElement = currentElement.parentElement;
+          if (currentElement === null) {
+            return null;
+          }
         }
         return null;
       };