Exception when retrieving contacts from Google Contacts API
public class Syncer {

private String consumerKey = "XXXXXXXXX";
private String consumerSecret = "XXXXXXXXX";
private String masterUser = "XXXXXXXXX";
private GoogleOAuthParameters oauthParameters;
private ContactsService contactService;
private AppsPropertyService appsService;


public Syncer() throws IOException, ServiceException, OAuthException {
    oauthParameters = new GoogleOAuthParameters();
    oauthParameters.setOAuthConsumerKey(consumerKey);
    oauthParameters.setOAuthConsumerSecret(consumerSecret);
    oauthParameters.setOAuthType(OAuthType.TWO_LEGGED_OAUTH);
    contactService = new ContactsService(consumerKey);
    contactService.setOAuthCredentials(oauthParameters, new OAuthHmacSha1Signer());
    appsService = new AppsPropertyService(consumerKey);
    appsService.setUserCredentials("XXXXXXX", "XXXXXXXXX");
    sync();
}

public List<ContactGroupEntry> retrieveGroups(String user) throws IOException, ServiceException {
    URL feedUrl = new URL("https://www.google.com/m8/feeds/groups/" + user + "/full?xoauth_requestor_id=" + masterUser);
    ContactGroupFeed resultFeed = contactService.getFeed(feedUrl, ContactGroupFeed.class);
    return resultFeed.getEntries();
}

public List<ContactEntry> retrieveGroupContacts(ContactGroupEntry group) throws IOException, ServiceException {
    URL feedUrl = new URL("https://www.google.com/m8/feeds/contacts/default/full?group=" + group.getId() + "&xoauth_requestor_id=" + masterUser);
    ContactFeed resultFeed = contactService.getFeed(feedUrl, ContactFeed.class);
    return resultFeed.getEntries();
}

public List<GenericEntry> getAllUsers() throws AppsForYourDomainException, MalformedURLException, IOException, ServiceException {
    GenericFeed feed = appsService.getFeed(new URL("https://apps-apis.google.com/a/feeds/user/2.0/" + consumerKey), GenericFeed.class);
    List<GenericEntry> users = feed.getEntries();
    Link next;
    while((next = feed.getNextLink()) != null) {
        feed = appsService.getFeed(new URL(next.getHref()), GenericFeed.class);
        users.addAll(feed.getEntries());
    }
    return users;
}


public void sync() throws IOException, ServiceException {
    Map<ContactGroupEntry, List<ContactEntry>> masterContactsList = new HashMap<ContactGroupEntry, List<ContactEntry>>();
    List<ContactGroupEntry> masterGroups = retrieveGroups(masterUser);
    ContactGroupFeed groupBatchCreate = new ContactGroupFeed();

    for(ContactGroupEntry group : masterGroups) {
        if(!group.hasSystemGroup() && group.getTitle().getPlainText().startsWith("SOG:")) {
            List<ContactEntry> contacts = retrieveGroupContacts(group);
            masterContactsList.put(group, contacts);

            ContactGroupEntry createContactGroup = new ContactGroupEntry();
            createContactGroup.setTitle(new PlainTextConstruct(group.getPlainTextContent()));
            BatchUtils.setBatchId(createContactGroup, "create");
            BatchUtils.setBatchOperationType(createContactGroup, BatchOperationType.INSERT);
            groupBatchCreate.getEntries().add(createContactGroup);
        }
    }

    List<GenericEntry> users = getAllUsers();
    for(GenericEntry user : users) {
        List<ContactGroupEntry> userGroups = retrieveGroups(user.getProperty("userEmail"));
        for(ContactGroupEntry group : userGroups) {
            if(group.getTitle().getPlainText().startsWith("SOG:")) {
                group.delete();
            }
        }

        contactService.batch(new URL("https://www.google.com/m8/feeds/groups/" + user.getProperty("userEmail") + "/full/batch"), groupBatchCreate);
    }
}


public static void main(String[] args) throws IOException, ServiceException, OAuthException {
    new Syncer();
}