get Firebase data and place it in RecyclerView

I am getting Firebase data, since I have debugged and in the getValue the data appears without any problem, but when I want to assign it to homes, the fields are null

This is the main code where I get the data from Firebase and try to add it to an adapter

   myDatabase.getRoot().addValueEventListener(new ValueEventListener() {
       @Override
       public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
           casasList.removeAll(casasList);
           for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
               Casas casas = childSnapshot.getValue(Casas.class);
               casasList.add(casas);
           }
           adapter.notifyDataSetChanged();
       }

I also add the Casas class where they have their constructors and their methods getters and setters public class Casas {     String mail, sale, purchase, address, id;

public Casas(String correo, String venta, String compra, String direccion) {
    this.correo = correo;
    this.venta = venta;
    this.compra = compra;
    this.direccion = direccion;
}

public Casas() {

}

public String getCorreo() {
    return correo;
}

public void setCorreo(String correo) {
    this.correo = correo;
}

public String getVenta() {
    return venta;
}

public void setVenta(String venta) {
    this.venta = venta;
}

public String getCompra() {
    return compra;
}

public void setCompra(String compra) {
    this.compra = compra;
}

public String getDireccion() {
    return direccion;
}

public void setDireccion(String direccion) {
    this.direccion = direccion;
}

}

This is the class where I build my adapter

public class RecyclerViewAdapter extends RecyclerView.Adapter {

ArrayList<Casas> casasList;

public RecyclerViewAdapter(ArrayList<Casas> casasList) {
    this.casasList = casasList;
}

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

@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
    Casas casa = casasList.get(position);
    holder.compra.setText(casa.getCompra());
    holder.venta.setText(casa.getVenta());
    holder.direccion.setText(casa.getDireccion());
}

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