передать данные из Realm в RecyclerView

Получаю данные из json и записываю их в БД Realm, как мне их потом передать в RecyclerView ?

Feed.java

public class Feed extends Fragment {
    private final String TAG = "log_tag";
    private Realm realm;
    private RealmResults<Article> art;
    private RecyclerView recyclerView;
    private SwipeRefreshLayout swipeRefreshLayout;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.feed_recycler_view, container, false);
        recyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
        swipeRefreshLayout = (SwipeRefreshLayout) view.findViewById(R.id.swipeRefreshLayout);
        swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                ResponseColumn();
            }
        });
        Realm.init(getActivity());
        RealmConfiguration config = new RealmConfiguration.Builder().build();
        Realm.setDefaultConfiguration(config);
        ResponseColumn();
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
        recyclerView.setAdapter(new RecyclerViewAdapter(art)); //в этой строке показывает ошибку
        return view;
    }
    private void ResponseColumn() {
        Gson gson = new GsonBuilder().setExclusionStrategies(new ExclusionStrategy() {
            @Override
            public boolean shouldSkipField(FieldAttributes f) {
                return f.getDeclaredClass().equals(RealmObject.class);
            }
            @Override
            public boolean shouldSkipClass(Class<?> clazz) {
                return false;
            }
        }).create();
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("https://newsapi.org/v1/articles/")
                .addConverterFactory(GsonConverterFactory.create(gson))
                .build();
        EngadgetAPI engadgetAPI = retrofit.create(EngadgetAPI.class);
        Call<EngadgetArticle> call = engadgetAPI.getArticle();
        call.enqueue(new Callback<EngadgetArticle>() {
            @Override
            public void onResponse(Call<EngadgetArticle> call, Response<EngadgetArticle> response) {
                realm = Realm.getDefaultInstance();
                realm.beginTransaction();
                //realm.deleteAll();
                List<Article> article = realm.copyToRealmOrUpdate(response.body().getArticles());
                realm.commitTransaction();
                art = realm.where(Article.class).findAll();
                Log.d(TAG, "onResponse: article = " + article.size());
                Log.d(TAG, "onResponse: realm size = " + art.size());
                Log.d(TAG, "onResponse: " + response.message());
            }
            @Override
            public void onFailure(Call<EngadgetArticle> call, Throwable t) {
                Log.d(TAG, "onFailure: " + t.getMessage());
            }
        });
        swipeRefreshLayout.setRefreshing(false);
    }
    @Override
    public void onDestroy() {
        super.onDestroy();
        realm.close();
    }
}

RecyclerViewAdapter.java

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder> implements RealmChangeListener<RealmResults<Article>> {
    private final RealmResults<Article> articles;
    public RecyclerViewAdapter(RealmResults<Article> articles) {
        this.articles = articles;
        this.articles.addChangeListener(this);//здесь тоже показывает ошибку
    }
    @Override
    public void onChange(RealmResults<Article> element) {
        notifyDataSetChanged();
    }

    class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
        CardView cardView;
        ImageView imageView;
        TextView tvTitle;
        TextView tvDescription;
        TextView tvPublished;
        ViewHolder(View view) {
            super(view);
            cardView = (CardView) view.findViewById(R.id.card_view);
            imageView = (ImageView) view.findViewById(R.id.imageView);
            tvTitle = (TextView) view.findViewById(R.id.tvTitle);
            tvDescription = (TextView) view.findViewById(R.id.tvDescription);
            tvPublished = (TextView) view.findViewById(R.id.tvPublished);
        }
        @Override
        public void onClick(View view) {
        }
    }
    @Override
    public RecyclerViewAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.card_view, parent, false);
        return new ViewHolder(view);
    }
    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        holder.tvTitle.setText(articles.get(position).getTitle());
        holder.tvDescription.setText(articles.get(position).getDescription());
        holder.tvPublished.setText(articles.get(position).getPublishedAt());
        Picasso.with(holder.cardView.getContext())
                .load(articles.get(position).getUrlToImage())
                .error(android.R.drawable.ic_menu_report_image)
                .into(holder.imageView);
        holder.cardView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
            }
        });
    }
    @Override
    public int getItemCount() {
        return articles.size();
    }
}

UPD ошибка

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.nikolai.engadgetnews, PID: 900
                  java.lang.NullPointerException: Attempt to invoke virtual method 'int io.realm.RealmResults.size()' on a null object reference
                      at com.example.nikolai.engadgetnews.RecyclerViewAdapter.getItemCount(RecyclerViewAdapter.java:85)
                      at android.support.v7.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:3416)
                      at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:3252)
                      at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:3767)
                      at android.view.View.layout(View.java:16630)
                      at android.view.ViewGroup.layout(ViewGroup.java:5437)
                      at android.support.v4.widget.SwipeRefreshLayout.onLayout(SwipeRefreshLayout.java:636)
                      at android.view.View.layout(View.java:16630)
                      at android.view.ViewGroup.layout(ViewGroup.java:5437)
                      at android.support.design.widget.CoordinatorLayout.layoutChild(CoordinatorLayout.java:1167)
                      at android.support.design.widget.CoordinatorLayout.onLayoutChild(CoordinatorLayout.java:852)
                      at android.support.design.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:871)
                      at android.view.View.layout(View.java:16630)
                      at android.view.ViewGroup.layout(ViewGroup.java:5437)
                      at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
                      at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
                      at android.view.View.layout(View.java:16630)
                      at android.view.ViewGroup.layout(ViewGroup.java:5437)
                      at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
                      at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
                      at android.view.View.layout(View.java:16630)
                      at android.view.ViewGroup.layout(ViewGroup.java:5437)
                      at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1079)
                      at android.view.View.layout(View.java:16630)
                      at android.view.ViewGroup.layout(ViewGroup.java:5437)
                      at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
                      at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
                      at android.view.View.layout(View.java:16630)
                      at android.view.ViewGroup.layout(ViewGroup.java:5437)
                      at android.support.v7.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:437)
                      at android.view.View.layout(View.java:16630)
                      at android.view.ViewGroup.layout(ViewGroup.java:5437)
                      at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
                      at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
                      at android.view.View.layout(View.java:16630)
                      at android.view.ViewGroup.layout(ViewGroup.java:5437)
                      at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1743)
                      at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1586)
                      at android.widget.LinearLayout.onLayout(LinearLayout.java:1495)
                      at android.view.View.layout(View.java:16630)
                      at android.view.ViewGroup.layout(ViewGroup.java:5437)
                      at android.widget.FrameLayout.layoutChildren(FrameLayout.java:336)
                      at android.widget.FrameLayout.onLayout(FrameLayout.java:273)
                      at com.android.internal.policy.PhoneWindow$DecorView.onLayout(PhoneWindow.java:2678)
                      at android.view.View.layout(View.java:16630)
                      at android.view.ViewGroup.layout(ViewGroup.java:5437)
                      at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2171)
                      at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1931)
                      at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
                      at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
                      at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
                      at android.view.Choreographer.doCallbacks(Choreographer.java:670)
                      at android.view.Choreographer.doFrame(Choreographer.java:606)
                      at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
                      at android.os.Handler.handleCallback(Handler.java:739)
                      at android.os.Handler.dispatchMessage(Handler.java:95)
                      at android.os.Looper.loop(Looper.java:148)
                      at android.app.ActivityThread.main(ActivityThread.java:5417)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                    at com.an