Uncaught TypeError: Cannot read property 'documentElement' of null

I have the newest Wampserver and i want to perform this simple tutorial: https://developers.google.com/maps/articles/phpsqlajax_v3, but when i want to display the result map on localhost, the Chrome, IE 11 and Firefox gives this error: Uncaught TypeError: Cannot read property 'documentElement' of null. I uploaded the HTML, PHP files and a picture of the error to gdrive: https://drive.google.com/folderview?id=0B_hF8gtVKKTld0pSSVpRN053MFk&usp=sharing I hope you can help me! Thanks in advance!