private void cancelSubscriptionToPEPService(JID unsubscriber, JID serviceOwner) {
        // Retrieve recipientJID's PEP service, if it exists.
        PEPService pepService = pepServiceManager.getPEPService(serviceOwner.asBareJID(), false);
        if (pepService == null) {
            return;
        }

        // Cancel unsubscriberJID's subscription to recipientJID's PEP service, if it exists.
        CollectionNode rootNode = pepService.getRootCollectionNode();
        NodeSubscription nodeSubscription = rootNode.getSubscription(unsubscriber);
        if (nodeSubscription != null) {
            rootNode.cancelSubscription(nodeSubscription);
        }
    }
Cancels a subscription to a PEPService's root collection node.

@param unsubscriber the JID of the subscriber whose subscription is being canceled.
@param serviceOwner the JID of the owner of the PEP service for which the subscription is being canceled.
xmppserver/src/main/java/org/jivesoftware/openfire/pep/IQPEPHandler.java