java.lang.NullPointerException: Attempt to invoke virtual method boolean java.lang.String.equals(java.lang.Object)' on a null object reference

Вот мои ошибки

Process: com.example.mydom, PID: 16108
    java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
        at com.example.mydom.Fragments.UsersFragment$3.onDataChange(UsersFragment.java:117)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75)
        at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)

Мой код User Adapter

public class UserAdapter  extends RecyclerView.Adapter<UserAdapter.ViewHolder>{
    private Context mContext;
    private List<User> mUsers;
    private boolean ischat;
    public UserAdapter(Context mContext,List<User> mUsers, boolean ischat){
        this.mUsers = mUsers;
        this.mContext = mContext;
        this.ischat = ischat;
    }

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

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
 User user = mUsers.get(position);
holder.username.setText(user.getUsername());
if (user.getImageURL().equals("default")){
    holder.profile_image.setImageResource(R.mipmap.ic_launcher);
}else{
    Glide.with(mContext).load(user.getImageURL()).into(holder.profile_image);
}
if(ischat){
    if(user.getStatus().equals("online")){
        holder.img_on.setVisibility(View.VISIBLE);
        holder.img_off.setVisibility(View.GONE);
    }else{
        holder.img_on.setVisibility(View.GONE);
        holder.img_off.setVisibility(View.VISIBLE);
    }
}else{
    holder.img_on.setVisibility(View.GONE);
    holder.img_off.setVisibility(View.GONE);
}
holder.itemView.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Intent intent = new Intent(mContext, MessageActivity.class);
        intent.putExtra("userid",user.getId());
        mContext.startActivity(intent);
    }
});
    }

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

    public class  ViewHolder extends RecyclerView.ViewHolder{
        public TextView username;
        public ImageView profile_image;

        private ImageView img_on;
        private ImageView img_off;


        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            username = itemView.findViewById(R.id.username);
            profile_image = itemView.findViewById(R.id.profile_image);
            img_on = itemView.findViewById(R.id.img_on);
            img_off = itemView.findViewById(R.id.img_off);
        }
    }
}

мой UsersFragment

public class UsersFragment extends Fragment {

private RecyclerView recyclerView;
private UserAdapter userAdapter;
private List<User> mUsers;

EditText search_users;


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_users,container,false);
recyclerView = view.findViewById(R.id.recycler_view);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
mUsers = new ArrayList<>();
readUsers();

search_users = view.findViewById(R.id.search_users);
search_users.addTextChangedListener(new TextWatcher() {
    @Override
    public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {

    }

    @Override
    public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
        searchUsers(charSequence.toString());

    }

    @Override
    public void afterTextChanged(Editable s) {

    }
});
        return view;
    }

    private void searchUsers(String s) {

        FirebaseUser fuser = FirebaseAuth.getInstance().getCurrentUser();
        Query query = FirebaseDatabase.getInstance().getReference("Users").orderByChild("search")
                .startAt(s)
                .endAt(s+"\uf8ff");
        query.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot datasnapshot) {
                mUsers.clear();
                for (DataSnapshot snapshot : datasnapshot.getChildren() ){
                    User user = snapshot.getValue(User.class);

                    assert user != null;
                    assert fuser != null;
                    if(!user.getId().equals(fuser.getUid())){
                        mUsers.add(user);
                    }
                }
                userAdapter = new UserAdapter(getContext(),mUsers,false);
                recyclerView.setAdapter(userAdapter);
            }

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

            }
        });
    }

    private void readUsers() {
        FirebaseUser firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
        DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Users");
        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot datasnapshot) {
                if (search_users.getText().toString().equals("")) {
                    mUsers.clear();
                    for (DataSnapshot snapshot : datasnapshot.getChildren()) {
                        User user = snapshot.getValue(User.class);
                        assert user != null;
                        assert firebaseUser != null;

                        if (!user.getId().equals(firebaseUser.getUid())) {
                            mUsers.add(user);
                        }
                    }
                    userAdapter = new UserAdapter(getContext(), mUsers, false);
                    recyclerView.setAdapter(userAdapter);
                }
            }

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

            }
        });
    }
}

Буду очень благодарен тому кто поможет.