"L'application s'est arrêté" dès que je cliques sur un bouton

package com.quizzfouta.gn;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import java.util.Random;

public class Main2Activity extends AppCompatActivity {



    private Questions mQuestions = new Questions();
    private TextView mScoreView;
    private TextView mQuestionView;
    private Button mButtonChoice1;
    private Button mButtonChoice2;
    private Button mButtonChoice3;
    private Button btnquit;

    private String mAnswer;
    private int mScore = 0;
    private int mQuestionNumber = 0;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        mButtonChoice1= (Button) findViewById(R.id.btn1);
        mButtonChoice2= (Button) findViewById(R.id.btn2);
        mButtonChoice3= (Button) findViewById(R.id.btn3);
        btnquit= (Button) findViewById(R.id.btnquit);
        mScoreView= (TextView) findViewById(R.id.score);
        mQuestionView= (TextView) findViewById(R.id.tvq);

        updateQuestion();

     // Debut des boutons Ecouteurs

        //Ecouteurs bouton 1
        mButtonChoice1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (mButtonChoice1.getText()== mAnswer){
                    mScore = mScore + 1;
                    updateScore(mScore);
                    updateQuestion();
                    //On ajoute un toast
                    Toast.makeText(Main2Activity.this, "C'est correct", Toast.LENGTH_SHORT).show();
                    } else {
                    Toast.makeText(Main2Activity.this, "C'est faux", Toast.LENGTH_SHORT).show();
                    updateQuestion();

                }
            }
        });
        //Ecouteurs Bouton 2
        mButtonChoice2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (mButtonChoice2.getText()== mAnswer){
                    mScore = mScore + 1;
                    updateScore(mScore);
                    updateQuestion();
                    //On ajoute un toast
                    Toast.makeText(Main2Activity.this, "C'est correct", Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(Main2Activity.this, "C'est faux", Toast.LENGTH_SHORT).show();
                    updateQuestion();

                }
            }
        });

        //Ecouteurs bouton 3
        mButtonChoice3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (mButtonChoice3.getText()== mAnswer){
                    mScore = mScore + 1;
                    updateScore(mScore);
                    updateQuestion();
                    //On ajoute un toast
                    Toast.makeText(Main2Activity.this, "C'est correct", Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(Main2Activity.this, "C'est faux", Toast.LENGTH_SHORT).show();
                    updateQuestion();

                }
            }
        });
        //Fin des écouteurs

    }

    private void updateQuestion() {

        mQuestionView.setText(mQuestions.getQuestions(mQuestionNumber));
        mButtonChoice1.setText(mQuestions.getChoice1(mQuestionNumber));
        mButtonChoice2.setText(mQuestions.getChoice2(mQuestionNumber));
        mButtonChoice3.setText(mQuestions.getChoice3(mQuestionNumber));

        mAnswer = mQuestions.getCorrectAnswer(mQuestionNumber);
        mQuestionNumber++;
    }

    private void updateScore(int point){
        mScoreView.setText("" + mScore);
    }
}