'java.lang.String java.lang.Object.toString ()' on a null object reference (Firebase)

Question

I tried to get extras from the intent in recyclerView and display it in detail but when I tried it there was a

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

public class NotifDetailAct extends AppCompatActivity {

DatabaseReference reference;
TextView xdeskripsi;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_notif_detail);

    xdeskripsi = (TextView) findViewById(R.id.xdeskripsi);

    Bundle bundle = getIntent().getExtras();
    final String tittle_baru = bundle.getString("tittle");


    reference = FirebaseDatabase.getInstance().getReference().child("notif").child(tittle_baru);
    reference.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            xdeskripsi.setText(dataSnapshot.child("isi_notif").getValue().toString());
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

}

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