How do I get UID of the value from custom attribute of type contributor

I am trying to get UID of value in a custom attribute  through a Java script  for using in customization through Java script.
Using the link below as reference.
https://jazz.net/wiki/bin/view/Main/AttributeCustomizationExamples
Section : Get an item's UUID (users, iterations, project areas)

I am able to get the UID  of contributor type using built in attribute with the following script 1.
script 1
=====================================================
dojo.provide("org.example.OwnerID");
dojo.require("com.ibm.team.workitem.api.common.WorkItemAttributes");

(function() {
var WorkItemAttributes= com.ibm.team.workitem.api.common.WorkItemAttributes;

dojo.declare("org.example.OwnerID", null, {

    getValue: function(attributeId, workItem, configuration) {
        return workItem.getValue(WorkItemAttributes.OWNER);
    }
});
})();
=========================================================

Trying get the UID of custom attribute using script 2 below.
script 2
==========================================================
dojo.provide("org.example.QAVerifierID");
dojo.require("com.ibm.team.workitem.api.common.WorkItemAttributes");

(function() {
var WorkItemAttributes= com.ibm.team.workitem.api.common.WorkItemAttributes;

dojo.declare("org.example.QAVerifierID", null, {

    getValue: function(attributeId, workItem, configuration) {
        return workItem.getValue("custom.workitem.attribute.QAVerifier");
    }
});
})();
===========================================================
QAVerifier is a custom attribute of type  contributor. 

Nothing populates  with the attribute linked to this script  for calculated value when I change the QAVerifier value and save it.

Any thoughts on what is wrong here ?   or is there a  other way to get UID ?