Try this

function onLoad() {

var userObject;
var name = g_form.getReference('mrb_on_behalf_of');
if (name ==null || name == '' ){
userObject = g_form.getReference('u_requestor',setUserInfo);}
else {
userObject = g_form.getReference('mrb_on_behalf_of',setUserInfo);}

function setUserInfo(userObject){
g_form.setValue('division',userObject.u_division);
g_form.setValue('position_title_02',userObject.title);
g_form.setValue('department',userObject.department);

}


}