element-ui 2.9.2 Cascader expand-change 方法不被调用

[hongweishang]

Cascader
expand-change 方法不被调用

  <el-form-item label="地区" prop="zone">
    <el-cascader
      v-model="selected"
      :options="zone_list"
      :props="props"
      @expand-change="handleItemChange" />
  </el-form-item>

  props: {
    value: 'id',
    label: 'name',
    children: 'children',
    expandTrigger: 'hover'
  },