unable to resolve class "import net.sf.json.xml.XMLSerializer in Ready APi 2.3.0

//Importing Packages.
import groovy.json.JsonSlurper;
import java.sql.*;
import com.eviware.soapui.SoapUI.*;
import net.sf.json.JSONSerializer;
import net.sf.json.xml.XMLSerializer;
import net.sf.json.JSON;
import net.sf.json.JSONObject;
import java.util.HashMap;
import java.util.Map;
import java.util.Iterator;
import java.math.*;
import java.util.List;

def tC = testRunner.getTestCase();
def tS = tC.getTestSuite();
def tP = tS.getProject();
def tStep = tC.getTestStepByName('get-ConfigEndpointDetails');
def dbUsername = context.expand( '${#Project#dbUsername}' );
def dbPassword = context.expand( '${#Project#dbPassword}' );
def dbHost = context.expand( '${#Project#targetSystem}' );
def siteType = context.expand( '${#TestCase#siteType}' );
def endpointId = context.expand( '${#TestCase#endpointId}' );

def httpContentType = context.expand( '${#TestCase#httpContentType}' )

//Extracting http status from testCase.
def httpStatus = context.expand( '${#TestCase#httpStatus}' )
log.info "httpStatus is: ----> "+ httpStatus;

if(httpStatus == "HTTP/1.1 500 Internal Server Error")
{

if ( httpContentType == "application/json;charset=UTF-8")
{

//Extracting response.
def responseAsJson = tStep.httpRequest.response.getResponseContent();
log.info responseAsJson

//Conversion from json to xml
def jsontoxml;
XMLSerializer xmlSerializer = new XMLSerializer();
JSON json = JSONSerializer.toJSON(responseAsJson);
xmlSerializer.setTypeHintsEnabled(false);
jsontoxml = xmlSerializer.write( json );
log.info "JSON Response converted to XML Response Result:" + jsontoxml;

//Parsing response by XmlSlurper.
def parsed_xml = new XmlSlurper().parseText(jsontoxml);
log.info "parsed_json Details : " + parsed_xml;

this causing failure