Can someone tell me why the submitList() method can't be accessed in the following code? Similar code is working fine in another test app, although that's in an Activity. 

```
public class MyFFBooksFragment extends Fragment {

       private int currentBook;
       private RecyclerView mRecyclerView;
       private RecyclerView.LayoutManager mLayoutManager;
       private GamebookViewModel gamebookViewModel;

       @Nullable
       @Override
       public View onCreateView(@NonNull LayoutInflater inflater, @Nullable 
       ViewGroup container, @Nullable Bundle savedInstanceState) {

               View view = inflater.inflate(R.layout.myffbooks_fragment, container, false);

               mLayoutManager = new LinearLayoutManager(getActivity());

               final ArrayList<BookItem> bookList = new ArrayList<>();
               final BookItemAdapter maAdapter = new BookItemAdapter(bookList);

               mRecyclerView = view.findViewById(R.id.recyclerView);
               mRecyclerView.setLayoutManager(mLayoutManager);
               mRecyclerView.setHasFixedSize(true);
               mRecyclerView.setAdapter(maAdapter);

               gamebookViewModel = ViewModelProviders.of(this).get(GamebookViewModel.class);
               gamebookViewModel.getAllGamebooks().observe(this, new Observer<List<Gamebook>>() {

               @Override
               public void onChanged(@Nullable List<Gamebook> gamebooks) {
                       maAdapter.submitList(bookList);
               }
           });

    return view;
   }
 }

```