问为什么我的RecyclerView上有一个空引用

EN

public class PagerAdapter extends FragmentPagerAdapter {

    private final String[] TITLES = {"Header 0", "Header 1" };

    public PagerAdapter(FragmentManager fm){
        super(fm);
    }

    @Override
    public CharSequence getPageTitle(int position){
        return TITLES[position];
    }

    @Override
    public int getCount() {
        return TITLES.length;
    }

    @Override
    public Fragment getItem(int position){
        switch(position){
            case 0:
                return new FragmentOne();
            case 1:
                return new FragmentTwo();
            default:
                return new FragmentOne();
        }
    }
}

public class FragmentOne extends Base {
    ... code for displaying content in the RecyclerView. Just contains my custom Adapter for the RecyclerView ...
}

public abstract class Base extends Fragment {

    public View mView;
    public RecyclerView mDataView;
    public ProgressBar mProgressBar;
    public Context mContext;
    private RecyclerView.LayoutManager mLayoutManager;

    public Base() { }

    @Override
    public View onCreateView(LayoutInflater _i, ViewGroup _vg, Bundle savedInstanceBundle){
        mView = _i.inflate(R.layout.f_base, null);
        mDataView = (RecyclerView) mView.findViewById(R.id.data);
        mProgressBar = (ProgressBar)mView.findViewById(R.id.loading);
        mLayoutManager = new LinearLayoutManager(mContext);
        mDataView.setLayoutManager(mLayoutManager);
        mContext = this.getActivity();
        return mView;
    }

    @Override
    public void onStart() {
        super.onStart();
        init();
        doWork();
    }

    public abstract void init();

    public abstract void doWork();

}

11-02 12:49:44.171    3708-3708/com.nitrox.digitune E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.nitrox.digitune, PID: 3708
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView$LayoutManager.stopSmoothScroller()' on a null object reference
            at android.support.v7.widget.RecyclerView.stopScrollersInternal(RecyclerView.java:1159)
            at android.support.v7.widget.RecyclerView.stopScroll(RecyclerView.java:1151)
            at android.support.v7.widget.RecyclerView.onDetachedFromWindow(RecyclerView.java:1356)
            at android.view.View.dispatchDetachedFromWindow(View.java:13441)
            at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2837)
            at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2834)
            at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:2834)
            at android.view.ViewGroup.removeViewInternal(ViewGroup.java:4163)
            at android.view.ViewGroup.removeViewInternal(ViewGroup.java:4136)
            at android.view.ViewGroup.removeView(ViewGroup.java:4068)
            at android.support.v4.view.ViewPager.removeView(ViewPager.java:1326)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1045)
            at android.support.v4.app.FragmentManagerImpl.detachFragment(FragmentManager.java:1280)
            at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:724)
            at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
            at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:486)
            at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:1073)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
            at android.support.v4.view.ViewPager$3.run(ViewPager.java:249)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
            at android.view.Choreographer.doCallbacks(Choreographer.java:580)
            at android.view.Choreographer.doFrame(Choreographer.java:549)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)