Android片段回调接口抛出null

您好,我有一个片段回调接口方法,它在Android 7.1.0上运行良好,但在Android 5.0.0中会引发此空异常。如何修复此问题?我感谢你的帮助。

代码

radioGroup.setOnCheckedChangeListener(new OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(RadioGroup group, int checkedId) {
            switch(checkedId)
            {
                case R.id.radio0:
                    answer = radio0.getText().toString();
                    break;
                case R.id.radio1:
                    answer = radio1.getText().toString();
                    break;
                case R.id.radio2:
                    answer = radio2.getText().toString();
                    break;
            }
        }
    });

@OnClick(R.id.button_submit)
public void submitAnswer()
{

    if(radioGroup.getCheckedRadioButtonId() != -1)
    {
        datapass(true, answer.toString());
    }
    radioGroup.clearCheck();
}



public void datapass(Boolean hasAnswer, String answer)
{
   fragmentCallBackInterface.passAnswer(hasAnswer, answer);
}

碎片回调接口

public interface FragmentCallBackInterface 
{
    public void passAnswer(boolean answerBool, String answerString);
}

实现接口的活动

public class QuizActivity extends BaseActivity implements 
FragmentCallBackInterface 
{
    boolean answerBool;
    String answerString;

    @Override
    public void passAnswer(boolean answerBool, String answerString)
    {
        this.answerBool = answerBool;
        this.answerString = answerString;

    }
}