markLine数值超出纵坐标最大值会消失echarts 折线配置项内容和展示

我给markLine传一个数值，当这个数值过大就会消失不见

      option = {
    title: {
        text: '自定义markLine数值',
    },
    tooltip: {
        trigger: 'axis'
    },
    legend: {
        data: ['最高气温']
    },
    toolbox: {
        show: true,
        feature: {
            dataZoom: {
                yAxisIndex: 'none'
            },
            dataView: {
                readOnly: false
            },
            magicType: {
                type: ['line', 'bar']
            },
            restore: {},
            saveAsImage: {}
        }
    },
    xAxis: {
        type: 'category',
        boundaryGap: false,
        data: ['周一', '周二', '周三', '周四', '周五', '周六', '周日']
    },
    yAxis: {
        type: 'value',
        axisLabel: {
            formatter: '{value} °C'
        }
    },
    series: [{
        name: '温度',
        type: 'line',
        data: [11, 11, 15, 13, 12, 13, 10],
        markLine: {
            itemStyle : { 
                    normal: { 
                        borderWidth:1, 
                        lineStyle: { 
                            type: 'dashed', //dotted、solid
                            color:'orange', 
                            width:2 
                        }, 
                    } 
                   
                }, 
            data: [{
                name: '固定横线',
                yAxis: 12
                //大于15就会消失
            }],
        }
    }]
};