Not sure how to fix error message: Attempt to invoke virtual method on a null reference

public Page(int imageId, int textId) {
    this.imageId = imageId;
    this.textId = textId;
    this.isFinalPage = true;
}

public Page(int imageId, int textId, Choice choice1, Choice choice2) {
    this.imageId = imageId;
    this.textId = textId;
    this.choice1 = choice1;
    this.choice2 = choice2;
}

public boolean isFinalPage() {
    return isFinalPage;
}

public void setFinalPage(boolean finalPage) {
    isFinalPage = finalPage;
}

public int getImageId(){
        return imageId;
}

public void setImageId(int imageId) {
    this.imageId = imageId;
}

public int getTextId() {
    return textId;
}

public void setTextId(int textId) {
    this.textId = textId;
}

public Choice getChoice1() {
    return choice1;
}

public void setChoice1(Choice choice1) {
    this.choice1 = choice1;
}

public Choice getChoice2() {
    return choice2;
}

public void setChoice2(Choice choice2) {
    this.choice2 = choice2;
}

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

    storyImageView = (ImageView) findViewById(R.id.storyImageView);
    storyTextView = (TextView)findViewById(R.id.storyTextView);
    choice1Button = (Button)findViewById(R.id.choice1);
    choice2Button = (Button)findViewById(R.id.choice2);

    Intent intent = getIntent();
    name = intent.getStringExtra(getString(R.string.key_name));
    if (name == null || name.isEmpty()) {
        name = "Friend";
    }
    story = new Story();
    loadPage(0);
}

private void loadPage(int pageNumber) {
    final Page page = story.getPage(pageNumber);

    Drawable image =ContextCompat.getDrawable(this, page.getImageId());
    storyImageView.setImageDrawable(image);

    String pageText = getString(page.getTextId());
    // Add name if placeholder included. Won't add if not
    pageText = String.format(pageText, name);
    storyTextView.setText(pageText);

    if (page.isFinalPage()){
        choice1Button.setVisibility(View.INVISIBLE);
        choice2Button.setText(getString(R.string.play_again_button_text));
    }else {
        loadButtons(page);
    }
}

private void loadButtons(final Page page) {
    choice1Button.setText(page.getChoice1().getTextId());
    choice1Button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
                int nextPage = page.getChoice1().getNextPage();
                loadPage(nextPage);
        }
    });
    choice2Button.setText(page.getChoice2().getTextId());
    choice2Button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            int nextPage = page.getChoice2().getNextPage();
            loadPage(nextPage);
        }
    });
}