notifyDataSetChanged() crash app when call

I am using Fragment to create a app which i can slide left and right to view questions. When i submit a question from another fragement it will update the 2nd listFragment/listView. However it always crash. Furthermore i tried storing stuff into the variable '"storeText"', it will be null after onActivityCreated.

import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.util.Log;
import android.widget.ArrayAdapter;

import java.util.ArrayList;



public class UserQuestion extends ListFragment {
    ArrayAdapter<String> adapter;
    private UserQuestionStorage storage = new UserQuestionStorage();
    private String storeText;

   @Override
   public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        //Set the list that was needed
        ArrayList<String> getQuestionList = storage.getQuestionList();
        this.adapter = new ArrayAdapter<String>(getActivity(),                       android.R.layout.simple_list_item_1, getQuestionList);

       //Test Storage
       this.storeQuestion(123, 1111, "Question 1", "true", "false");
       this.storeQuestion(123, 1111, "Question 2", "true", "false");

       storeText = "Storing this to variable.";

       setListAdapter(this.adapter);
    }

  public void storeQuestion(int id, int ownerID, String questionText, String optionOne, String optionTwo) {
      Question userQuestion = new Question();
      userQuestion.createQuestion(id, ownerID, questionText, optionOne, optionTwo);

      this.storage.storeQuestion(questionText);

      //TODO: This is not working
      Log.d("QUESTION", "" + this.storage.getQuestionList()); //Storage is always wipe.
      Log.d("ADAPTER", "" + adapter);
      Log.d("TESTSTRING", "" + storeText);
      //refreshList();
  }

  public void refreshList(){
      this.adapter.notifyDataSetChanged();
  }

}

via Chebli Mohamed