Android工作室Google加登录集成无法获得生日

Question

Person person = Plus.PeopleApi.getCurrentPerson(mGoogleApiClient);
String personName = person.getDisplayName();
String email = Plus.AccountApi.getAccountName(mGoogleApiClient);
String dob = person.getBirthday();
Toast.makeText(getBaseContext(), "You are Logged In " + personName+"" +email+" "+dob, Toast.LENGTH_LONG).show();

我已经尝试过这段代码来检索名称电子邮件和dob但不幸的是我没有得到dob它的null我得到了。请帮助