NullPointerException in resolverFactory.getServiceResourceResolver(param)

I am trying to access page properties using services in AEM 6.4

I have created  an interface,

public interface AccessPageProp {

public String getPageProp();

}

I have created a class that implements this interface,

@Component(service = AcccessPagePropImpl.class, immediate = true)

public class AcccessPagePropImpl implements AccessPageProp {

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

@Reference

private ResourceResolverFactory resolverFactory;

@Override

public String getPageProp() {

logger.info("Entering into getPageProp()...");

String title = "";

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

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

ResourceResolver resourceResolver = null;

try {

resourceResolver = resolverFactory.getServiceResourceResolver(param);

Resource pageResource = resourceResolver.getResource("/content/MyProject/en/TestPageName/jcr:content");

Page myPage = pageResource.adaptTo(Page.class);

title = myPage.getTitle();

return title;

} catch (Exception e) {

logger.info("Exception...."+e.toString());

e.printStackTrace();

}

return title;

}

}

I am getting "java.lang.NullPointerException" in line "resourceResolver = resolverFactory.getServiceResourceResolver(param);"