error

public class ChatsFragment extends Fragment {


    List<Chatslist> userlist;
    List<Users> mUsers;
    RecyclerView recyclerView;
    UserAdapter mAdapter;
    FirebaseUser firebaseUser;


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view =  inflater.inflate(R.layout.fragment_chats, container, false);


        userlist = new ArrayList<>();

        recyclerView = view.findViewById(R.id.chat_recyclerview_chatfrag);
        recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));


        firebaseUser = FirebaseAuth.getInstance().getCurrentUser();

        DatabaseReference reference  = FirebaseDatabase.getInstance().getReference("Chatslist")
                .child(firebaseUser.getUid());


        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {

                userlist.clear();
                for (DataSnapshot ds: snapshot.getChildren()) {
                    Chatslist chatslist = ds.getValue(Chatslist.class);

                    userlist.add(chatslist);
                }

                ChatsListings();
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {
            }
        });
        return view;
    }

    private void ChatsListings() {

        mUsers = new ArrayList<>();

        DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("Users");


        databaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {

                mUsers.clear();

                for (DataSnapshot ds: snapshot.getChildren()) {

                    Users users = ds.getValue(Users.class);

                    for (Chatslist chatslist: userlist) {

                        if (users.getId().equals(chatslist.getId())) {

                            mUsers.add(users);
                        }
                    }
                }

                mAdapter = new UserAdapter(getContext(), mUsers, true);
                recyclerView.setAdapter(mAdapter);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) { }
        });

    }
}