Найти ошибку в коде !

package com.example.myapplication;
 
import androidx.annotation.NonNull;
import androidx.annotation.RequiresApi;
import androidx.appcompat.app.AppCompatActivity;
import androidx.constraintlayout.widget.ConstraintLayout;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
 
import android.app.Activity;
import android.os.Build;
import android.os.Bundle;
import android.text.Layout;
import android.util.Log;
import android.view.View;
import android.widget.Adapter;
import android.widget.TextView;
 
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.xwray.groupie.GroupAdapter;
import com.xwray.groupie.GroupieViewHolder;
import com.xwray.groupie.Item;
 
import java.security.acl.Group;
import java.util.function.Consumer;
 
public class NewMessage extends AppCompatActivity {
    RecyclerView recyclerView;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_new_message);
        getSupportActionBar().setTitle("Select User");
        recyclerView=findViewById(R.id.recyclerView_newMessage);
        GroupAdapter adapter= new GroupAdapter<GroupieViewHolder>();
        fetchUsers(recyclerView);
 
        recyclerView.setAdapter(adapter);
    }
    private void fetchUsers(final View view){
       DatabaseReference ref=FirebaseDatabase.getInstance().getReference("/users");
       ref.addListenerForSingleValueEvent(new ValueEventListener() {
           @RequiresApi(api = Build.VERSION_CODES.N)
           @Override
           public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
               final GroupAdapter adapter=new GroupAdapter<GroupieViewHolder>();
               dataSnapshot.getChildren().forEach(new Consumer<DataSnapshot>() {
                   @Override
                   public void accept(DataSnapshot dataSnapshot) {
                       Log.d("TAG", "accept: "+dataSnapshot.toString());
                       User user= dataSnapshot.getValue(User.class);
                       //if(user!=null){
                         //  adapter.add(new UserItem(user,view));
                       //}
                       Log.d("Main", "accept: "+user);
 
                   }
               });
               recyclerView.setAdapter(adapter);
           }
 
           @Override
           public void onCancelled(@NonNull DatabaseError databaseError) {
 
           }
       });
    }
}
class UserItem extends Item<GroupieViewHolder> {
    User user;
    TextView text_username;
    View view;
 
    public UserItem(User user, View view) {
        this.view=view;
        this.user = user;
        text_username=view.findViewById(R.id.textView_newmessage);
    }
 
 
    @Override
    public void bind(@NonNull GroupieViewHolder viewHolder, int position) {
        text_username.setText(user.getUsername());
 
    }
 
    @Override
    public int getLayout() {
        return R.layout.user_row_new_message;
    }
}

class User{
    public String uid;
    public String username;
    public String profileImageUrl;
 
    public User(String s, String s1, String s2) {
        this.uid=s;
        this.username=s1;
        this.profileImageUrl=s2;
    }
 
    public void setUid(String uid) {
        this.uid = uid;
    }
 
    public void setUsername(String username) {
        this.username = username;
    }
 
    public void setProfileImageUrl(String profileImageUrl) {
        this.profileImageUrl = profileImageUrl;
    }
 
    public String getUid() {
        return uid;
    }
 
    public String getUsername() {
        return username;
    }
 
    public String getProfileImageUrl() {
        return profileImageUrl;
    }
}