Users not registering in database

Question

private void register (String username, String email, String password) {
    auth.createUserWithEmailAndPassword(email,password)
            .addOnCompleteListener(task -> {
                if (task.isSuccessful()){
                    FirebaseUser firebaseUser = auth.getCurrentUser();
                    String userid = firebaseUser.getUid();

                    reference = FirebaseDatabase.getInstance().getReference("users").child(userid);

                    HashMap<String, String> hashMap = new HashMap<>();
                    hashMap.put("id",userid);
                    hashMap.put("username",username);
                    hashMap.put("imageURL","default");

                    reference.setValue(hashMap).addOnCompleteListener(new OnCompleteListener<Void>() {
                        @Override
                        public void onComplete(@NonNull Task<Void> task) {
                            if (task.isSuccessful()){
                                Intent intent = new Intent(RegisterActivity.this,MainActivity.class);
                                intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
                                startActivity(intent);
                                finish();
                            }
                        }
                    });
                } else{
                    Toast.makeText(RegisterActivity.this, "You can't register with this email and password", Toast.LENGTH_SHORT).show();
                }
            });

Users are not showing in my database after registering using this code.