如果缓存为空,则对NPE进行改装

我添加了缓存的可能性,并且会发生以下脚本: 如果以前上传过页面,一切正常,但是如果我第一次没有互联网 然后应用程序崩溃并引发错误

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 n.MainDetailTrainFragment$3.onResponse(MainDetailTrainFragment.java:171)

我理解这个错误,但我如何修复它?

不要严格判断,我只是在学习。 这是我的密码^

progressBarTrain.setVisibility(View.VISIBLE);
    Log.d(TAG, "getProducts");

   final OkHttpClient client = new OkHttpClient
           .Builder()
           .cache(new Cache(getActivity().getCacheDir(), 10 * 1024 * 1024)) // 10 MB
           .addInterceptor(new Interceptor() {
               @Override public okhttp3.Response intercept(@NonNull Chain chain) throws IOException {
                   Request request = chain.request();
                   if (NetworkUtils.isNetworkAvailable(getActivity())) {
                       request = request.newBuilder().header("Cache-Control", "public, max-age=" + 60).build();
                   } else {
                       request = request.newBuilder().header("Cache-Control", "public, only-if-cached, max-stale=" + 60 * 60 * 24 * 7).build();
                   }
                   return chain.proceed(request);
               }
           })
           .build();

    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(MY_URL)
            .client(client)
            .addConverterFactory(SimpleXmlConverterFactory.create())
            .build();

    retrofit.create(myTrainInterface.class)
            .getProducts(APP_ID, FROM_CITY, position_0, "everyday")
            .enqueue(new Callback<Responce>() {
                @SuppressLint("SetTextI18n")
                @Override
                public void onResponse(@NonNull Call<Responce> call, @NonNull Response<Responce> response) {
                    progressBarTrain.setVisibility(View.INVISIBLE);
                    if (response.body() != null) {
                        kk = response.body().products;
                    }
                    ArrayList<Responce.Item> p = new ArrayList<>(kk);
                    String s = String.valueOf(response.body());




                    adapter = new DetailTrainAdapter(p);
                    recyclerView.setAdapter(adapter);
                    Log.d(TAG, s);

                    textError.setVisibility(TextView.INVISIBLE);
                    textErrorRestart.setVisibility(TextView.INVISIBLE);
                }

                @Override
                public void onFailure(@NonNull Call<Responce> call, @NonNull Throwable throwable) {
                    Log.d(TAG, "onFailure" + throwable.getLocalizedMessage());
                    textError();
                }
            });