Проблема с FirebaseRecyclerAdapter, on a null object reference

Отображение из БД Firebase работает нормально, но когда пытаюсь удалить элемент из базы приложение вылетает, хотя удаление происходит. Пишет on a null object reference в строке String postDescription = dataSnapshot.child("desc").getValue().toString(); Вот мой код:

public class PostFragment extends Fragment {
private RecyclerView recyclerPost;
private DatabaseReference postReference;
private View view;
private LinearLayoutManager layoutManager;
public PostFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, final ViewGroup container, Bundle savedInstanceState) {
    view = inflater.inflate(R.layout.fragment_post, container, false);
    recyclerPost = view.findViewById(R.id.recycler_post);
    postReference = FirebaseDatabase.getInstance().getReference().child("Posts");
    postReference.keepSynced(true);
    layoutManager = new LinearLayoutManager(getContext());
    layoutManager.setReverseLayout(true);
    layoutManager.setStackFromEnd(true);
    recyclerPost.setHasFixedSize(true);
    recyclerPost.setLayoutManager(layoutManager);
    return view;
}
@Override
public void onStart() {
    super.onStart();
    Query query = postReference.orderByChild("timestamp");
    FirebaseRecyclerOptions<Posts> options =
            new FirebaseRecyclerOptions.Builder<Posts>()
                    .setQuery(query, Posts.class)
                    .build();
    FirebaseRecyclerAdapter adapter = new FirebaseRecyclerAdapter<Posts, PostViewHolder>(options) {
        @Override
        protected void onBindViewHolder(@NonNull final PostViewHolder holder, int position, @NonNull final Posts model) {
            final String postId = getRef(position).getKey();
            postReference.child(postId).addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    String postDescription = dataSnapshot.child("desc").getValue().toString();
                    holder.postDesc.setText(postDescription);                   
                }
                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {
                }
            });
            holder.delBtn.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    postReference.child(postId).removeValue();
                }
            });

        }
        @NonNull
        @Override
        public PostViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int position) {
            View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.blog_item, viewGroup, false);
            return new PostViewHolder(view);
        }
    };
    adapter.startListening();
    recyclerPost.setAdapter(adapter);
}
public class PostViewHolder extends RecyclerView.ViewHolder {
    private TextView postDesc;
    private Button delBtn;
    private View view;
    public PostViewHolder(@NonNull View itemView) {
        super(itemView);
        view = itemView;
        postDesc = (TextView) view.findViewById(R.id.post_description); 
        delBtn = (Button) view.findViewById(R.id.del_post_btn);
    }
}
}

Подскажите пожалуйста решение данной проблемы.