HTTP filtered based value set not retrieving the values in the combo box

Hello Team,

I am new to RTC attribute customization. I was trying the HTTP filtered based value set on one basic example :

dojo.provide("org.example.workitems.providers.CDCatalogValueSet");
dojo.require("com.ibm.team.workitem.api.common.connectors.HttpConnectorParameters");

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

dojo.declare("org.example.workitems.providers.CDCatalogValueSet", null, {

    getFilteredValueSet: function(attributeId, workItem, context, filter) {

        var params= new com.ibm.team.workitem.api.common.connectors.HttpConnectorParameters();
        params.url= "http://www.w3schools.com/xml/cd_catalog.xml";
        params.xpath= "//CD";
        params.columnXpaths= ["./ARTIST"];
        params.columnIds= ["ARTIST"];

        var connector= context.getDataConnector("HttpConnector");
        var values= connector.get(params);

        var result= [];
        while(values.hasNext()){
            var entry= values.next();
            var title= entry.getById("ARTIST");
            if (title.indexOf(filter) > -1) {
                result.push(title);
            }
        }

        return result;
    }
});
})(); 

I have also created the attribute with Medium HTML datatype. but when I see in the UI, I see the empty dropdown with no values, it displays "retrieving". however there are values in http://www.w3schools.com/xml/cd_catalog.xml.

Could you please assist me on this.