radar图的tooltip对象里面的trigger: 'axis'不起作用echarts radar配置项内容和展示

将radar图的tooltip对象的trigger设置为 'axis'时，tooltip显示不出来，是否是radar图不能设置tooltip对象的trigger属性为'axis'。

      option = {
    legend: {
          itemWidth: 14,
          icon: 'path://M100 100 L100 150 L125 193.30127 L150 150 L150 100 L125 56.69873Z',
          y: 'bottom',
          x: 'center',
          data: ['年级得分率', '高一（2）班得分率'],
          itemGap: 28
        },

        tooltip: {
          show: true,
          trigger: 'item',
          borderWidth: 1,
          borderColor: '#56b1f5'
        },

        toolbox: {
          show: true,
          feature: {
            saveAsImage: {
              show: true,
              iconStyle: {
                normal: {
                  borderColor: '#12bf50'
                },
                emphasis: {
                  borderColor: '#12bf50'
                }
              }
            }
          },
          right: 30
        },

        radar: {
          shape: 'circle',
          name: {
            textStyle: {
              color: '#fff',
              backgroundColor: '#12bf50',
              borderRadius: 3,
              padding: [3, 3]
            }
          },
          indicator: [
            { name: '二次函数', max: 100, axisLabel: {show: true, fontSize: 12}},
            { name: '解析数学', max: 100},
            { name: '多项式', max: 100},
            { name: '数组', max: 100},
            { name: '不等式证明', max: 100},
            { name: '集合', max: 100}
          ],
          center: [ '50%', '52%']
        },

        series: [{
          type: 'radar',
          data: [
            {
              value: [40, 34, 28, 35, 50, 19],
              name: '年级得分率'
            },
            {
              value: [50, 14, 28, 31, 42, 21],
              name: '高一（2）班得分率'
            }
          ]
        }]
};