E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.santossingh.capstoneproject, PID: 9157
                                                                                   java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object[] java.util.Collection.toArray()' on a null object reference
                                                                                       at java.util.ArrayList.<init>(ArrayList.java:171)
                                                                                       at com.santossingh.capstoneproject.Fragments.BaseFragment$1.onResponse(BaseFragment.java:113)
                                                                                       at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:68)
                                                                                       at android.os.Handler.handleCallback(Handler.java:751)
                                                                                       at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                       at android.os.Looper.loop(Looper.java:154)
                                                                                       at android.app.ActivityThread.main(ActivityThread.java:6077)
                                                                                       at java.lang.reflect.Method.invoke(Native Method)
                                                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                                                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

public class BaseFragment extends Fragment {

    RecyclerView recyclerView;
    private RetrofitManager retrofitManager;
    private List<Work> resultsList;
    private GRecyclerViewAdapter recyclerViewAdapter;
    private View view;
    private OnFragmentInteractionListener mListener;

    public BaseFragment() {
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        view= inflater.inflate(R.layout.fragment_base, container, false);

        resultsList=new ArrayList<Work>();
        configRecycleView();
        makeService();
        return view;
    }

    private void configRecycleView() {
        recyclerViewAdapter = new GRecyclerViewAdapter(getContext(), resultsList, mListener);
        recyclerView = (RecyclerView) view.findViewById(R.id.recycleView);
        AutofitGridlayout autofitGridlayout = new AutofitGridlayout(getActivity(), 260);
        recyclerView.setLayoutManager(autofitGridlayout);
        recyclerView.setAdapter(recyclerViewAdapter);
    }
    public void makeService() {
        retrofitManager=new RetrofitManager();
        Call<Results> listCall;
        listCall = retrofitManager.getXMLData().getBooks();
        listCall.enqueue(new Callback<Results>() {
            @Override
            public void onResponse(Call<Results> call, Response<Results> response) {
                if (response.isSuccessful()) {
                    List<Work> work=response.body().getWorks();
                    resultsList=new ArrayList<Work>(work);

                    if (resultsList != null) {
                        recyclerViewAdapter.addList(resultsList);
                        Toast.makeText(getContext(), "XML Successfully fetched", Toast.LENGTH_LONG).show();
                    } else {
                        Toast.makeText(getActivity(), "Null Value", Toast.LENGTH_SHORT).show();
                    }
                }
            }
            @Override
            public void onFailure(Call<Results> call, Throwable t) {
                Toast.makeText(getContext(), t.getMessage(), Toast.LENGTH_LONG).show();
                Log.e("error",t.getMessage());
                t.printStackTrace();
            }
        });
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    public interface OnFragmentInteractionListener {
        void onFragmentInteraction(Work mData);
        void onFragmentInteraction(Item mData);
    }
}

public class GRecyclerViewAdapter extends RecyclerView.Adapter<GRecyclerViewAdapter.ViewHolder> {

    private List<Work> workList=new ArrayList<Work>();

    private BaseFragment.OnFragmentInteractionListener mListener;
    private Context context;
    private float AspectRatio = 0.73f;

    public GRecyclerViewAdapter(Context context, List<Work> itemList, BaseFragment.OnFragmentInteractionListener listener) {
        this.context = context;
        workList=itemList;
        mListener = listener;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.fragment_item, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(final ViewHolder holder, final int position) {

        holder.work = workList.get(position);
        holder.dynamicImageView.setImageUrl((holder.work.getImage()),
                ImageLoaderHelper.getInstance(context).getImageLoader());
        holder.dynamicImageView.setAspectRatio(AspectRatio);
        holder.mIdView.setText(holder.work.getTitle());

        holder.mView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if (null != mListener) {
                    // Notify the active callbacks interface (the activity, if the
                    // fragment is attached to one) that an item has been selected.
                    mListener.onFragmentInteraction(holder.work);
                }
            }
        });
    }

    @Override
    public int getItemCount() {
        return workList.size();
    }

    public void addList(List<Work> workList) {
        this.workList = workList;
        notifyDataSetChanged();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        public final View mView;
        public final TextView mIdView;
        private final DynamicHeightNetworkImageView dynamicImageView;
        private Work work;

        public ViewHolder(View view) {
            super(view);
            mView = view;
            dynamicImageView = (DynamicHeightNetworkImageView) view.findViewById(R.id.thumbnail);
            mIdView = (TextView) view.findViewById(R.id.Title);
        }
    }
}

@Root (name = "results", strict = false)
public class Results {

    @ElementList(required = false)
    public List<Work> works;

    public Results(List<Work> works) {
        this.works = works;
    }
    public List<Work> getWorks() {
        return works;
    }
    public void setWorks(List<Work> works) {
        this.works = works;
    }

    public Results() {
    }
}

@Root(name = "work", strict = false)
public class Work {

    @Path("best_book")
    @Element(name = "id")
    private String id;

    @Path("best_book")
    @Element (name = "title")
    private String title;

    @Path("best_book/author")
    @Element(name = "name")
    private String author;

    @Path("best_book")
    @Element (name = "image_url")
    private String image;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public String getImage() {
        return image;
    }

    public void setImage(String image) {
        this.image = image;
    }

    public Work(String id, String title, String author, String image) {
        this.id = id;
        this.title = title;
        this.author = author;
        this.image = image;
    }
}

public class RetrofitManager implements GoodReadsService{

    public static final String API_BASE_URL = "https://www.goodreads.com/";
    private GoodReadsAPI goodReadsAPI;

    public void RetrofitOutput(){
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(API_BASE_URL)
                .client(new OkHttpClient())
                .addConverterFactory(SimpleXmlConverterFactory.create())
                .build();
        if (retrofit!=null){
            Log.i("Data Fetch","Yes");
        }

        goodReadsAPI=retrofit.create(GoodReadsAPI.class);
        if (goodReadsAPI!=null){
            Log.i("Data","Yes");
        }else {
            Log.e("Error","No");
        }

    }

    @Override
    public GoodReadsAPI getXMLData() {
        if (goodReadsAPI==null){
            RetrofitOutput();
        }
        return goodReadsAPI;
    }
}

public interface GoodReadsAPI {
    @GET(Constants.path+Constants.apiKey+Constants.BUSINESS)
    Call<Results> getBooks();
}

public interface GoodReadsService {
    GoodReadsAPI getXMLData();
}