How to fetch RTC work item change sets using plain java api?

Question

I am trying to fetch the changes using below code but every time it returns null. I don't know what is wrong with this code.

ILinkManager fLinkManager = (ILinkManager) repo.getClientLibrary(ILinkManager.class);
        IReferenceFactory fReferenceFactory = fLinkManager.referenceFactory();
        IReference reference = fReferenceFactory.createReferenceToItem(workItem.getItemHandle());

        ILinkQueryPage page = fLinkManager.findLinksByTarget("com.ibm.team.filesystem.workitems.change_set", reference,
                monitor);
        ILinkCollection linkCollection = page.getAllLinksFromHereOn();
        Collection<ILink> links = linkCollection.getLinksById("com.ibm.team.filesystem.workitems.change_set");