How to set ProgressBar value using this code?

Question

I've two values in my document which will help me to set progress bar in the app. for ex joined and slots. both are numbers.

and below i am fetching the values and setting the progressbar value using the slots and joined number which i fetched from the firestore :

public class Home extends AppCompatActivity {
    private FirebaseFirestore mDatabase;
    private FirestoreRecyclerAdapter adapter;
    RecyclerView recyclerView;

    @Override
    protected void onStart() {
        super.onStart();
        adapter.startListening();
    }

    @Override
    protected void onStop() {
        super.onStop();
        adapter.stopListening();
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        FirebaseAuth mAuth = FirebaseAuth.getInstance();
        FirebaseUser mUser = mAuth.getCurrentUser();
        mDatabase = FirebaseFirestore.getInstance();

        recyclerView = findViewById(R.id.rv);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));

        if (mUser != null) {
            fetch();
        } else {
            Intent intent = new Intent(Home.this, Login.class);
            startActivity(intent);
            finish();
        }
    }

private void fetch() {
            Query query = mDatabase.collection("batches");
            FirestoreRecyclerOptions<batches> options = new FirestoreRecyclerOptions.Builder<batches>()
                    .setQuery(query, new SnapshotParser<batches>() {
                        @NonNull
                        @Override
                        public matches parseSnapshot(@NonNull DocumentSnapshot snapshot) {
                            return new matches(                             
                                    snapshot.getLong("slots"),
                                    snapshot.getLong("joined")
                            );
                        }
                    }).build();

            adapter = new FirestoreRecyclerAdapter<batches,BatchHolder>(options) {
                @Override
                protected void onBindViewHolder(@NonNull BatchHolder holder, int position, @NonNull batches model) {
                    holder.progressBar.setProgress(model.getJoined().intValue()/model.getSlots().intValue()*100);
                }

                @NonNull
                @Override
                public BatchHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
                    View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.list_items,viewGroup,false);
                    return new BatchHolder(view);
                }
            };
            recyclerView.setAdapter(adapter);
        }
public class BatchHolder extends RecyclerView.ViewHolder {
            ProgressBar progressBar;
            public BatchHolder(@NonNull View itemView) {
                super(itemView);
                progressBar = itemView.findViewById(R.id.progressBar);
            }
        }  

and in batches.class :

public class batches {
    private Long slots, joined;

    public matches(Long slots, Long joined) {
        this.slots = slots;
        this.joined = joined;
    } 

    public Long getSlots() {
        return slots;
    }

    public void setSlots(Long slots) {
        this.slots = slots;
    }

    public Long getJoined() {
        return joined;
    }

    public void setJoined(Long joined) {
        this.joined = joined; 
    }

but when i run the app it says the following error :

    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ProgressBar.setProgress(int)' on a null object reference
        at app.Home$2.onBindViewHolder(Home.java:109)
        at app.Home$2.onBindViewHolder(Home.java:100)
        at com.firebase.ui.firestore.FirestoreRecyclerAdapter.onBindViewHolder(FirestoreRecyclerAdapter.java:125)
        at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6781)
        at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6823)
        at android.support.v7.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:5752).... so on