Android Setting Up Credential Using Google API

I want to create an Android application and using Google People Api. I followed all the steps on this tutorial: https://developers.google.com/people/v1/getting-started.

So I created a new project in Google Api Console, get the client id and client secret for a web application, set the consent screen oauth. Finally I tried to run the google code that use can see in the above link, but I get an Exception on creating "GoogleTokenResponse".

I post the exception even if I don't find it useful:

Process: simone.biliato.testpeopleapi, PID: 13067
java.lang.RuntimeException: Unable to start activity ComponentInfo{simone.biliato.testpeopleapi/simone.biliato.testpeopleapi.MainActivity}: java.lang.NullPointerException
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2658)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2723)
    at android.app.ActivityThread.access$900(ActivityThread.java:172)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:145)
    at android.app.ActivityThread.main(ActivityThread.java:5832)
    at java.lang.reflect.Method.invoke(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:372)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
 Caused by: java.lang.NullPointerException
    at com.google.api.client.repackaged.com.google.common.base.Preconditions.checkNotNull(Preconditions.java:770)
    at com.google.api.client.util.Preconditions.checkNotNull(Preconditions.java:127)
    at com.google.api.client.auth.oauth2.AuthorizationCodeTokenRequest.setCode(AuthorizationCodeTokenRequest.java:147)
    at com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeTokenRequest.setCode(GoogleAuthorizationCodeTokenRequest.java:147)
    at com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeTokenRequest.setCode(GoogleAuthorizationCodeTokenRequest.java:79)
    at com.google.api.client.auth.oauth2.AuthorizationCodeTokenRequest.<init>(AuthorizationCodeTokenRequest.java:103)
    at com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeTokenRequest.<init>(GoogleAuthorizationCodeTokenRequest.java:111)
    at com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeTokenRequest.<init>(GoogleAuthorizationCodeTokenRequest.java:92)
    at simone.biliato.testpeopleapi.MainActivity.setUp(MainActivity.java:63)
    at simone.biliato.testpeopleapi.MainActivity.onCreate(MainActivity.java:27)
    at android.app.Activity.performCreate(Activity.java:6221)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2611)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2723) 
    at android.app.ActivityThread.access$900(ActivityThread.java:172) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 

Has anyone had the same? Is there any working example? I need to use "Google Button Sign-in"?

I think you can try and use the following example: https://github.com/sdivakarrajesh/Google-Drive-Java-API

It's for Google Drive Api but you can use the code for permission and then change the scopes.