I am getting error "Error in data(): "TypeError: Unable to get property 'questions' of undefined or null reference" found in---> Questions> at resources\assets\js\components\Questions.vue"

What I'm doing wrong here component is not rendered on the page. I am trying to add component from here

     `<template>
<div class="ques_wrapper">
	<div v-for="(question, index) in quiz.questions" class="ques_block">
		
	</div>
</div>

export default { data() { return { quiz: { title: 'My quiz', questions: [ { text: "Question 1", responses: [ {text: 'Wrong, too bad.'}, {text: 'Right!', correct: true}, ] }, { text: "Question 2", responses: [ {text: 'Right answer', correct: true}, {text: 'Wrong answer'}, ] } ] }, questionIndex: 0, userResponses: Array(this.quiz.questions.length).fill(false) } },

    // The view will trigger these methods on click

    methods: {

      // Go to next question

      next: function() {

        this.questionIndex++;

      },

      // Go to previous question

      prev: function() {

        this.questionIndex--;

      },

      // Return "true" count in userResponses

      score: function() {

        return this.userResponses.filter(function(val) { return val }).length;

      }

    }

}

 </script>`