Не отображается кастомный adapter в List на базе Firebase

Пытаюсь вывести данные из Firebase, но выдает пустой лист. Не понимаю в че причина, так как делал все по гайду. Помогите пожалуйста, уже не понимаю, что мне делать.

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.os.Bundle;
import com.firebase.ui.database.FirebaseRecyclerOptions;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.Query;

public class MainActivity extends AppCompatActivity {

    private RecyclerView recyclerView;
    personAdapter
            adapter; // Create Object of the Adapter class
    DatabaseReference mbase; // Create object of the
    // Firebase Realtime Database

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

        // Create a instance of the database and get
        // its reference
        mbase
                = FirebaseDatabase.getInstance().getReference();

        recyclerView = findViewById(R.id.recycler1);

        // To display the Recycler view linearly
        recyclerView.setLayoutManager(
                new LinearLayoutManager(this));

        // It is a class provide by the FirebaseUI to make a
        // query in the database to fetch appropriate data
        FirebaseRecyclerOptions<person> options
                = new FirebaseRecyclerOptions.Builder<person>()
                .setQuery(mbase, person.class)
                .build();
        // Connecting object of required Adapter class to
        // the Adapter class itself
        adapter = new personAdapter(options);
        // Connecting Adapter class with the Recycler view*/
        recyclerView.setAdapter(adapter);
    }

    // Function to tell the app to start getting
    // data from database on starting of the activity
    @Override protected void onStart()
    {
        super.onStart();
        adapter.startListening();
    }

    // Function to tell the app to stop getting
    // data from database on stopping of the activity
    @Override protected void onStop()
    {
        super.onStop();
        adapter.stopListening();
    }
}

Класс адаптера

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.firebase.ui.database.FirebaseRecyclerOptions;

// FirebaseRecyclerAdapter is a class provided by
// FirebaseUI. it provides functions to bind, adapt and show
// database contents in a Recycler View
public class personAdapter extends FirebaseRecyclerAdapter<
        person, personAdapter.personsViewholder> {

    public personAdapter(
            @NonNull FirebaseRecyclerOptions<person> options)
    {
        super(options);
    }

    // Function to bind the view in Card view(here
    // "person.xml") iwth data in
    // model class(here "person.class")
    @Override
    protected void
    onBindViewHolder(@NonNull personsViewholder holder,
                     int position, @NonNull person model)
    {

        // Add firstname from model class (here
        // "person.class")to appropriate view in Card
        // view (here "person.xml")
        holder.firstname.setText(model.getFirstname());

        // Add lastname from model class (here
        // "person.class")to appropriate view in Card
        // view (here "person.xml")
        holder.lastname.setText(model.getLastname());

        // Add age from model class (here
        // "person.class")to appropriate view in Card
        // view (here "person.xml")
        holder.age.setText(model.getAge());
    }

    // Function to tell the class about the Card view (here
    // "person.xml")in
    // which the data will be shown
    @NonNull
    @Override
    public personsViewholder
    onCreateViewHolder(@NonNull ViewGroup parent,
                       int viewType)
    {
        View view
                = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.person, parent, false);
        return new personAdapter.personsViewholder(view);
    }

    // Sub Class to create references of the views in Crad
    // view (here "person.xml")
    class personsViewholder
            extends RecyclerView.ViewHolder {
        TextView firstname, lastname, age;
        public personsViewholder(@NonNull View itemView)
        {
            super(itemView);

            firstname
                    = itemView.findViewById(R.id.firstname);
            lastname = itemView.findViewById(R.id.lastname);
            age = itemView.findViewById(R.id.age);
        }
    }
}

Класс person

public class person
{
    // Variable to store data corresponding
    // to firstname keyword in database
    private String firstname;

    // Variable to store data corresponding
    // to lastname keyword in database
    private String lastname;

    // Variable to store data corresponding
    // to age keyword in database
    private String age;

    // Mandatory empty constructor
    // for use of FirebaseUI
    public person() {}

    // Getter and setter method
    public String getFirstname()
    {
        return firstname;
    }
    public void setFirstname(String firstname)
    {
        this.firstname = firstname;
    }
    public String getLastname()
    {
        return lastname;
    }
    public void setLastname(String lastname)
    {
        this.lastname = lastname;
    }
    public String getAge()
    {
        return age;
    }
    public void setAge(String age)
    {
        this.age = age;
    }
}