Inicio de session de Google alternativo en android

Intentaba iniciar session en Android siguiendo los documentos y el código en Git . Pero obtengo un error ,

12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: FATAL EXCEPTION: main 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: Process: com.example.www.newapp, PID: 3098 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=40962, result=-1, data=Intent { (has extras) }} to activity {com.example.www.newapp/com.google.android.gms.auth.api.signin.internal.SignInHubActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at android.app.ActivityThread.deliverResults(ActivityThread.java:3699) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at android.app.ActivityThread.handleSendResult(ActivityThread.java:3742) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at android.app.ActivityThread.-wrap16(ActivityThread.java) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1393) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:102) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at android.os.Looper.loop(Looper.java:148) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5417) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at java.lang.reflect.Method.invoke(Native Method) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at java.util.Collections.sort(Collections.java:1896) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at com.google.android.gms.auth.api.signin.GoogleSignInAccount.zzms(Unknown Source) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at com.google.android.gms.auth.api.signin.GoogleSignInAccount.zzmx(Unknown Source) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at com.google.android.gms.auth.api.signin.internal.zzn.zza(Unknown Source) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at com.google.android.gms.auth.api.signin.internal.zzn.zzb(Unknown Source) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at com.google.android.gms.auth.api.signin.internal.SignInHubActivity.zza(Unknown Source) 12-17 13:55:43.287 3098-3098/com.example.www.newapp E/AndroidRuntime: at com.google.android.gms.auth.api.signin.internal.SignInHubActivity.onActivityResult(Unknown Source) 

entonces, ¿hay alguna manera alternativa de usar el inicio de session de Google en mi aplicación de Android? Ayuda apreciada