Script Include returning null

[Vijay485]

 I want a project account from employee table to catalog form

 whenever a user logs in his project account should be populated 

Client script 

function onLoad() {
//Type appropriate comment here, and begin script below
alert("hello script include");
var user = g_form.getValue('requested_by');
alert(user); // returning sys_id
var ga = new GlideAjax('ProjectAccount');
ga.addParam('sysparm_name','callback');
ga.addParam('sysparm_user','user');
ga.getXML(getDetails);
function getDetails(response){
var answer = response.responseXML.documentElement.getAttribute('answer');
alert(answer); // returning null
g_form.setValue('current.variables.project_account',answer);

}

Script include 

var ProjectAccount = Class.create();

ProjectAccount.prototype = Object.extendsObject(global.AbstractAjaxProcessor, {

    callback: function() {

        var user = this.getParameter('sysparm_user');

        var gr = new GlideRecord('x_1037697_corpor_0_employee');

        gr.addQuery('sys_id',gs.getUserID);

        gr.query();

        //gs.debug('E-voucher ='+gr.getRowCount);

        if (gr.next()) {

            var pa = gr.project_account;

//gs.info("pa acccount"+ pa);

gs.log("pa acccount"+ pa);

return pa;

        }

    },

[swathisarang98]

@Vijay485 ,Thanks for marking my answer as helpful. If it helped you in any way please accept the solution so that it will be beneficial to the future readers with the same query.