I am trying to run the Google People API [sample code](https://github.com/Suleiman19/People-API-App) by following the steps [here](http://blog.grafixartist.com/people-api-android-tutorial-2/). Unfortunately it's always got a null connections from `response.getConnections()` of ListConnectionsResponse. Below AsyncTask is executed in `onActivityResult` after sign in successful:

```
class PeoplesAsync extends AsyncTask<String, Void, List<String>> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        updateUI();
    }

    @Override
    protected List<String> doInBackground(String... params) {

        List<String> nameList = new ArrayList<>();

        try {
            People peopleService = PeopleHelper.setUp(MainActivity.this, params[0]);

            ListConnectionsResponse response = peopleService.people().connections()
                    .list("people/me").setRequestMaskIncludeField("person.names,person.emailAddresses,person.phoneNumbers")
                    .execute();
            List<Person> connections = response.getConnections();

            //error: connections is always null
            for (Person person : connections) {
                if (!person.isEmpty()) {
                    List<Name> names = person.getNames();
                    List<EmailAddress> emailAddresses = person.getEmailAddresses();
                    List<PhoneNumber> phoneNumbers = person.getPhoneNumbers();

                    if (phoneNumbers != null)
                        for (PhoneNumber phoneNumber : phoneNumbers)
                            Log.d(TAG, "phone: " + phoneNumber.getValue());

                    if (emailAddresses != null)
                        for (EmailAddress emailAddress : emailAddresses)
                            Log.d(TAG, "email: " + emailAddress.getValue());

                    if (names != null)
                        for (Name name : names)
                            nameList.add(name.getDisplayName());

                }
            }

        } catch (IOException e) {
            e.printStackTrace();
        }

        return nameList;
    }

    @Override
    protected void onPostExecute(List<String> nameList) {
        super.onPostExecute(nameList);

        progressBar.setVisibility(View.GONE);

        recyclerView.setVisibility(View.VISIBLE);

        adapter = new PeopleAdapter(nameList);
        recyclerView.setLayoutManager(new LinearLayoutManager(MainActivity.this));
        recyclerView.setAdapter(adapter);

    }
}

```

What are the reasons causing null response connections in Google People API and how to fix it?