Android: Cannot Resume

I am trying to integrate Twitter into my application. I want to show a popup where the user can enter their tweet.

Now that the user is already logged in, the app works fine, but if the user needs to log in first, the apps will open the Twitter login web interface. From there, I cannot go back to my application and show the "enter-tweet" popup.

Please, help.

Exception:
04-02 00:16:53.511: ERROR/AndroidRuntime(5992): java.lang.RuntimeException: Unable to resume activity {mad.android.MyTwitterApp/mad.android.MyTwitterApp.AndroidTwitterSample}: java.lang.NullPointerException
04-02 00:16:53.511: ERROR/AndroidRuntime(5992):     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3128)
04-02 00:16:53.511: ERROR/AndroidRuntime(5992):     at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3143)
04-02 00:16:53.511: ERROR/AndroidRuntime(5992):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2059)
04-02 00:16:53.511: ERROR/AndroidRuntime(5992):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-02 00:16:53.511: ERROR/AndroidRuntime(5992):     at android.os.Looper.loop(Looper.java:123)
04-02 00:16:53.511: ERROR/AndroidRuntime(5992):     at android.app.ActivityThread.main(ActivityThread.java:4627)
04-02 00:16:53.511: ERROR/AndroidRuntime(5992):     at java.lang.reflect.Method.invokeNative(Native Method)
04-02 00:16:53.511: ERROR/AndroidRuntime(5992):     at java.lang.reflect.Method.invoke(Method.java:521)
04-02 00:16:53.511: ERROR/AndroidRuntime(5992):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:871)
04-02 00:16:53.511: ERROR/AndroidRuntime(5992):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:629)
04-02 00:16:53.511: ERROR/AndroidRuntime(5992):     at dalvik.system.NativeStart.main(Native Method)