无法销毁活动java.lang.NullPointerException

Question

我在我的活动中使用动态片段，这是我的onCreate：

    @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_utente);           
        if(findViewById(R.id.framelayout2) != null){
            mDualFragments=true;
            ListUtente lu = new ListUtente();
            FragmentTransaction transaction = getSupportFragmentManager()
                    .beginTransaction();
            transaction.add(R.id.framelayout1, lu);
            transaction.commit();
            DettUtente du = new DettUtente();
            FragmentTransaction transaction1 = getSupportFragmentManager()
                    .beginTransaction();
            transaction1.add(R.id.framelayout2, du);
            transaction1.commit();           
        } else{         
                ListUtente lu = new ListUtente();
                lu.setArguments(getIntent().getExtras());
                getSupportFragmentManager().beginTransaction()
                .add(R.id.framelayout1, lu).commit();                       
        }               
}

我的问题是当我旋转设备时：

03-05 18:26:47.223: E/AndroidRuntime(14216): FATAL EXCEPTION: main
03-05 18:26:47.223: E/AndroidRuntime(14216): java.lang.RuntimeException: Unable to destroy activity {com.unipg.utente/com.unipg.utente.ActivityUtente}: java.lang.NullPointerException
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3401)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3419)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3617)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.app.ActivityThread.access$700(ActivityThread.java:144)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1216)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.os.Handler.dispatchMessage(Handler.java:99)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.os.Looper.loop(Looper.java:137)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.app.ActivityThread.main(ActivityThread.java:4966)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at java.lang.reflect.Method.invokeNative(Native Method)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at java.lang.reflect.Method.invoke(Method.java:511)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at dalvik.system.NativeStart.main(Native Method)
03-05 18:26:47.223: E/AndroidRuntime(14216): Caused by: java.lang.NullPointerException
03-05 18:26:47.223: E/AndroidRuntime(14216):    at com.unipg.utente.ListUtente.onDestroy(ListUtente.java:111)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.support.v4.app.Fragment.performDestroy(Fragment.java:1680)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1040)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1070)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.support.v4.app.FragmentManagerImpl.dispatchDestroy(FragmentManager.java:1898)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.support.v4.app.FragmentActivity.onDestroy(FragmentActivity.java:324)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.app.Activity.performDestroy(Activity.java:5172)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.app.Instrumentation.callActivityOnDestroy(Instrumentation.java:1109)
03-05 18:26:47.223: E/AndroidRuntime(14216):    at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3388)
03-05 18:26:47.223: E/AndroidRuntime(14216):    ... 12 more
03-05 18:30:31.543: E/Trace(14605): error opening trace file: No such file or directory (2)

如果我改变我的设备，我想动态修改我的片段。如果我写这个我没有上次错误（我破坏savedInstanceState）：

    @Override
protected void onCreate(Bundle savedInstanceState) {
    if (savedInstanceState != null) {
        savedInstanceState.remove("android:support:fragments");
    }

更新这是我的listFragment destroy ..

@Override
public void onDestroyView(){
    super.onDestroyView();
    // libera l'adapter e chiudo il thread
    setListAdapter(null);
    threadutenti.cancel(true);
}

没关系，但在我的应用程序中，我必须始终将savedInstanceState保存为空...我该怎么办？