Error in getServiceResourceResolver method

package com.x.x.core.workflow;

import java.util.Collections;

import java.util.HashMap;

import java.util.Map;

import javax.jcr.Node;

import javax.jcr.NodeIterator;

import javax.jcr.Session;

import javax.jcr.query.Query;

import javax.jcr.query.QueryManager;

import javax.jcr.query.QueryResult;

//import org.apache.felix.scr.annotations.Component;

import org.osgi.service.component.annotations.Component;

import org.apache.felix.scr.annotations.Properties;

import org.apache.felix.scr.annotations.Property;

import org.apache.felix.scr.annotations.Service;

import org.osgi.framework.Constants;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import com.adobe.granite.workflow.WorkflowException;

import com.adobe.granite.workflow.WorkflowSession;

import com.adobe.granite.workflow.exec.WorkItem;

import com.adobe.granite.workflow.exec.WorkflowProcess;

import com.adobe.granite.workflow.metadata.MetaDataMap;

import org.apache.felix.scr.annotations.Reference;

//Sling Imports

import org.apache.sling.api.resource.ResourceResolverFactory ;

import org.apache.sling.api.resource.ResourceResolver;

import com.day.cq.dam.api.AssetManager;

//This is a component so it can provide or consume services

@Properties({

    @Property(name = Constants.SERVICE_DESCRIPTION, value = "Draft to Final Move Assets Description"),

    @Property(name = Constants.SERVICE_VENDOR, value = "Adobe"),

    @Property(name = "process.label", value = "Draft to Final Move Assets Label") })

@Component(

    immediate = true,

    service = WorkflowProcess.class,

    configurationPid = "com.x.x.core.workflow.DraftToFinalMove"

)

public class DraftToFinalMove implements WorkflowProcess{

/** Default log. */

protected final Logger log = LoggerFactory.getLogger(this.getClass());

private Session session;         

//Inject a Sling ResourceResolverFactory

@Reference

private ResourceResolverFactory resolverFactory;

@Override

public void execute(WorkItem item, WorkflowSession wfsession,MetaDataMap args) throws WorkflowException {

log.info("**** execute method here");

Map<String, Object> param = new HashMap<String, Object>();

        param.put(ResourceResolverFactory.SUBSERVICE, "datawrite");

        ResourceResolver resourceResolver = null;

try{

//get Current assinee from workflow

String currentAssinee = item.getCurrentAssignee();

log.info("currentAssinee::"+currentAssinee);

String copyPath = null;

String assetPath = null;

ResourceResolver resourceResolver = resolverFactory.getServiceResourceResolver(param);

session = resourceResolver.adaptTo(Session.class);

com.adobe.granite.asset.api.AssetManager assetManager = resourceResolver.adaptTo(com.adobe.granite.asset.api.AssetManager.class);

QueryManager qm = session.getWorkspace().getQueryManager();

Query q = qm.createQuery("/jcr:root/content/dam/dal/bos-workflow/bga/draft//*[jcr:primaryType='dam:Asset']", "xpath");

QueryResult result = q.execute();

NodeIterator nIt = result.getNodes();

StringBuilder output = new StringBuilder();

log.info("assetPath:2: ");

while (nIt.hasNext()) {

Node node = nIt.nextNode();

assetPath = "/content/dam/dal/bos-workflow/bga/draft/"+node.getName();

copyPath = "/content/dam/dal/bos-workflow/bga/final/"+node.getName();

assetManager.moveAsset(assetPath, copyPath);

}

// Log out

session.save();

session.logout();

log.info("Successfully Moved the Assets!!!");

}

catch(Exception e)

{

log.error("exceptionb::::",e);

}

}

}