Не могу обновить адаптер RecyclerView данными, полученными из Livedata в другом потоке

Приложение падает с NPE в методе getItemCount(). Ошибка -

Process: com.example.fridge_project, PID: 18634 
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference.

На закомментированном участке по сути то же самое работает. Как можно поменять адаптер из другого потока?

public class ProductsActivity extends AppCompatActivity {

private RecyclerView productsRecycler ;
private ImageButton addProduct ;
private FridgeRepository fridgeRepository;
private MutableLiveData<List<FoodData>> foodList ;
private ArrayList<FoodData> testList ;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_products);

    initTestList();

    addProduct = findViewById(R.id.addProduct);
    productsRecycler = findViewById(R.id.recyclerProducts);
    LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this, RecyclerView.VERTICAL, false);
    productsRecycler.setAdapter(new ProductsAdapter(testList));
    productsRecycler.setLayoutManager(linearLayoutManager);

    initRepo(this);

//        foodList = new MutableLiveData<>();
//        ArrayList<FoodData> m = new ArrayList<>();
//        foodList.setValue(m);
//        ArrayList<FoodData> n = (ArrayList<FoodData>) foodList.getValue();
//        productsRecycler.setAdapter(new ProductsAdapter(n));
}

@Override
protected void onDestroy() {
    super.onDestroy();
    closeRepo();
}

private void initRepo(final Context context) {
    Thread thread = new Thread(new Runnable() {
        @Override
        public void run() {
            fridgeRepository = new FridgeRepository(ProductsActivity.this) ;
            foodList = fridgeRepository.getFoodDataList();

            List<FoodData> foodData = new ArrayList<>() ;
            MutableLiveData<List<FoodData>> k = new MutableLiveData<>();
            k.postValue(foodData);
            ArrayList<FoodData> foodData1 = (ArrayList<FoodData>) k.getValue() ;
            productsRecycler.setAdapter(new ProductsAdapter(foodData1));
        }
    });
    thread.start();
}

private void closeRepo() {
    fridgeRepository = null ;
}

private void initTestList() {
    FoodData foodData1 = new FoodData("Name1", 2.0) ;
    FoodData foodData2 = new FoodData("Name2", 2.0) ;
    FoodData foodData3 = new FoodData("Name3", 2.0) ;
    testList = new ArrayList<>();
    testList.add(foodData1) ;
    testList.add(foodData2) ;
    testList.add(foodData3) ;
}

class ProductsAdapter extends RecyclerView.Adapter<ProductsAdapter.ProductsViewHolder>{

    List<FoodData> rFoodList ;

    ProductsAdapter(List<FoodData> list) {
        rFoodList = list ;
    }

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

    @Override
    public void onBindViewHolder(@NonNull ProductsViewHolder holder, int position) {
        holder.bindData(rFoodList.get(position));
    }

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

    public void changeList(LiveData<ArrayList<FoodData>> newList) {
        rFoodList = newList.getValue();
    }

    class ProductsViewHolder extends RecyclerView.ViewHolder {

        private TextView productName ;
        private TextView productAmount ;

        public ProductsViewHolder(@NonNull View itemView) {
            super(itemView);
            productName = itemView.findViewById(R.id.productName) ;
            productAmount = itemView.findViewById(R.id.productAmount) ;
        }

        void bindData(FoodData foodData) {
            productName.setText(foodData.getName());
            productAmount.setText(foodData.getAmount().toString());
        }
    }
}
}