getting form:options value in AJAX

Jsp code is as follows:

<form:select id="taxId" path="taxSeqNo" cssClass="defaultText"        <form:options items="${taxListItemsBean.taxList}" itemValue="key" itemLabel="label"/>
</form:select>

Where ${taxListItemsBean.taxList} is declared as

private List<KeyItemDto> taxList;

in the form.java class.

I want to pass this taxList through ajax to controller. Code in Ajax is:

//..
var options = {
                url: "${pageContext.request.contextPath}/abc.html",
                dataType : 'json',
                contentType:'application/json',
                data: JSON.stringify(taxList ),
                beforeSubmit: function(data,set,options) {
                    if(!confirm("xxx?")) {
                        return false;
                    }
                },

..//

Controller code:

@RequestMapping(value = "/abc.html", method = RequestMethod.POST)
    public ModelAndView executeConfirmTaxHttpServletRequest request,
      , @RequestBody List<KeyItemDto> taxList) {

System.out.println("taxList "+taxList);

}

With the above code im getting a NPE in Ajax at this line :

data: JSON.stringify(taxList ),

Not sure what is wrong with the code and how would it get passed to controller and retrieved. Any inputs appreciated.