使用vue获取豆瓣电影的某个电影详细信息，数据已经获取成功，average属性也在页面上显示成功，但是控制台却报错。

<template>
    <p id="movie-detail">
        <p class="movie-card">
            <h2>{{detail.title}}</h2>
            <h4>({{detail.original_title}})</h4>
            <section class="movie-intro">
                <p class="left">
                <!--就是这部分代码报错-->
                    <mt-cell>
                        <span v-if='detail.rating.average!=0'>{{detail.rating.average}}分</span>
                        <span v-else>暂无评分</span>
                        <img v-for="starNum in Math.round(detail.rating.average/2)" slot="icon" src="../../static/images/ratingStar.png" width="18" height="18">
                    </mt-cell>
                </p>
            </section>
        </p>
    </p>
</template>
<script>
export default {
    data() {
            return {
                movieID: '',
                detail: []
            }
        },
        created: function() {
            var that = this;
            this.$http.get('http://127.0.0.1:8081/movie/subject/' + that.$route.params.id)
                .then(function(response) {
                    that.detail = response.data;
                }).catch(function(error) {
                    console.log(error);
                });
        },
        mounted: function() {
            this.movieID = this.$route.params.id;
        }
}
</script>