AEM Workflow: getModel() method is throwing null value - aem

Question

I've created a new workflow model in the workflow console and trying to access it using a service. From the jsp I'm passing the workflow name as /etc/workflow/models/DeleteNode/jcr:content/model, followed the format mentioned in the AEM docs. But the WorkFlowModel is throwing null value while I try to get the model from the path that I've passed.
below is the service that I've written:
package com.aem.sample.workflow;
import java.util.Calendar;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.StringWriter;
import java.util.Iterator;
import java.util.List;
import java.util.ArrayList;
import java.io.InputStream;
import javax.jcr.Repository;
import javax.jcr.SimpleCredentials;
import javax.jcr.Node;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.apache.jackrabbit.commons.JcrUtils;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Service;
import javax.jcr.RepositoryException;
import org.apache.felix.scr.annotations.Reference;
import org.apache.jackrabbit.commons.JcrUtils;
import org.apache.sling.api.resource.ResourceResolver;
import org.apache.sling.api.resource.ResourceResolverFactory;
import org.apache.sling.jcr.api.SlingRepository;
import javax.jcr.Session;
import javax.jcr.Node;
//Adobe CQ Workflow APIs
import com.day.cq.workflow.model.WorkflowModel ;
import com.day.cq.workflow.WorkflowService ;
import com.day.cq.workflow.WorkflowSession;
import com.day.cq.workflow.exec.WorkflowData;
//Sling Imports
import org.apache.sling.api.resource.ResourceResolverFactory ;
import org.apache.sling.api.resource.ResourceResolver;
import org.apache.sling.api.resource.Resource;
//This is a component so it can provide or consume services
#Component
#Service
public class InvokeAEMWorkflowImp implements InvokeAEMWorkflow {
#Reference
private WorkflowService workflowService;
private Session session;
#Reference
private ResourceResolverFactory resolverFactory;
#Override
public String StartWorkflow(String workflowName, String workflowContent) {
try
{
//Invoke the adaptTo method to create a Session
ResourceResolver resourceResolver = resolverFactory.getAdministrativeResourceResolver(null);
session = resourceResolver.adaptTo(Session.class);
//Create a workflow session
WorkflowSession wfSession = workflowService.getWorkflowSession(session);
// Get the workflow model
WorkflowModel wfModel = wfSession.getModel(workflowName);
// Get the workflow data
// The first param in the newWorkflowData method is the payloadType. Just a fancy name to let it know what type of workflow it is working with.
WorkflowData wfData = wfSession.newWorkflowData("JCR_PATH", workflowContent);
// Run the Workflow.
wfSession.startWorkflow(wfModel, wfData);
return workflowName +" has been successfully invoked on this content: "+workflowContent ;
}
catch(Exception e)
{
e.printStackTrace();
}
return null;
}
}