(Android) NullPointerException if handler is not passed

[manumaticx]

If you do not pass a success or error calbback to the signin method the module will crash with a NullPointerEcxeption

07-31 15:28:16.491: E/AndroidRuntime(18057): java.lang.RuntimeException: An error occured while executing doInBackground()
07-31 15:28:16.491: E/AndroidRuntime(18057):    at android.os.AsyncTask$3.done(AsyncTask.java:304)
07-31 15:28:16.491: E/AndroidRuntime(18057):    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
07-31 15:28:16.491: E/AndroidRuntime(18057):    at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
07-31 15:28:16.491: E/AndroidRuntime(18057):    at java.util.concurrent.FutureTask.run(FutureTask.java:242)
07-31 15:28:16.491: E/AndroidRuntime(18057):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
07-31 15:28:16.491: E/AndroidRuntime(18057):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
07-31 15:28:16.491: E/AndroidRuntime(18057):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
07-31 15:28:16.491: E/AndroidRuntime(18057):    at java.lang.Thread.run(Thread.java:818)
07-31 15:28:16.491: E/AndroidRuntime(18057): Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object org.appcelerator.kroll.KrollFunction.call(org.appcelerator.kroll.KrollObject, java.util.HashMap)' on a null object reference
07-31 15:28:16.491: E/AndroidRuntime(18057):    at com.sitata.googleplus.TitaniumGooglePlusModule.handleSignInSuccess(TitaniumGooglePlusModule.java:232)
07-31 15:28:16.491: E/AndroidRuntime(18057):    at com.sitata.googleplus.TitaniumGooglePlusModule.access$000(TitaniumGooglePlusModule.java:44)
07-31 15:28:16.491: E/AndroidRuntime(18057):    at com.sitata.googleplus.TitaniumGooglePlusModule$FetchUserTokenTask.doInBackground(TitaniumGooglePlusModule.java:426)
07-31 15:28:16.491: E/AndroidRuntime(18057):    at android.os.AsyncTask$2.call(AsyncTask.java:292)
07-31 15:28:16.491: E/AndroidRuntime(18057):    at java.util.concurrent.FutureTask.run(FutureTask.java:237)
07-31 15:28:16.491: E/AndroidRuntime(18057):    ... 4 more