Issue 2647 fixed.
_include.js modified and issue 2647 fixed.
Changes made.
Add the isNull, isString, and isUndefined checks to _include.js

* Add unit tests for isNull and isUndefined
* remove the _ from is_Undefined and is_Null
Add tests for loggedInUser type when calling navigator.id.watch
Clean up the tests slightly
Merge pull request #3979 from shane-tomlinson/issue2647

Issue2647

A pleasure working through this with you, @mohit-agarwal! Thank you very much for the contribution! 

r+