resourceresolver null java.lang.NullPointerException

I'm getting java.lang.NullPointerException

Here's my code

package com.adobe.aem.xxx.screens.core;

import java.util.HashMap;

import java.util.Map;

import javax.annotation.PostConstruct;

//Sling Imports

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

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

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

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

import org.apache.sling.models.annotations.Model;

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

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

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

@Component(immediate=true)

@Model(adaptables = Resource.class)

public class DisplayLocation{

    Logger logger = LoggerFactory.getLogger(DisplayLocation.class);

    private String locationTitle;

    private String srcLocation;

    private String title = "No data";

    private String location = "/content/screens/xxx-screens/locations/xxx/xxx-displays/jcr:content";

    //Inject a Sling ResourceResolverFactory

    @Reference

    private ResourceResolverFactory resolverFactory;

    @PostConstruct

    protected void init() {

        logger.info("Post Construct Entrance");

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

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

        ResourceResolver resourceResolver = null;

        try {

            logger.info("ResourceResolver");

            logger.info("RF " + resolverFactory);

            title = param.toString();

            resourceResolver = resolverFactory.getServiceResourceResolver(param);   //this is the error. It then proceed to catch.

            logger.info(resourceResolver.getUserID());                                                       //lines from here isn't read.

            logger.info("Resource");

            Resource resource = resourceResolver.getResource(location);

            logger.info("ValueMap");

            ValueMap properties = resource.adaptTo(ValueMap.class);

            title = properties.get("sling:resourceType", String.class);

            resourceResolver.close();

        } catch (Exception e) {

            e.printStackTrace();

            logger.error("Error in Try Catch " + e);

        }

        locationTitle = title;

        srcLocation = location;

    }

    public String getLocationTitle() {

        return locationTitle;

    }

    public String getLocationTitle2() {

        return srcLocation;

    }

}

I've searched and searched but to no avail.

Apache Sling Service Mapper: (tried both)(and many more)

my system-user

Bundle Name:

Why do I get?