Uncaught TypeError: Cannot read property 'idd' of null

Having issue when saving xhtmlform,referred link for reference

       [code]  contactForm.attachEvent("onButtonClick", function(name, command){
		 if (id=='save'){
			 contactForm.save(); 
		    }
        });[/code]

Made entry in xml file also.

          [code]
[/code]

In the mentioned tutorial:
docs.dhtmlx.com/tutorials__first_app__index.html
The following xml data for the form is used:

	<item type="button" 	value="Submit" 		offsetTop="15" 	offsetLeft="230"/>

And the following code for the button click:

contactForm.attachEvent("onButtonClick", function(name, command){ contactForm.save(); //sends the values of the updated row to the server });