ant-design-vue select选择框无法显示placehoder

将绑定的对应值设置成undefined

<a-select
                  v-model:value="formState.classification"
                  option-filter-prop="children"
                  allow-clear
                  placeholder="商户分类"
                >
                  <a-select-option
                    v-for="item of Object.values(
                      Const.POINTMERCHNANDISE.TYPE_MAP
                    )"
                    :key="item.value"
                    :value="item.value"
                    >{{ item.text }}</a-select-option
                  >
                </a-select>
const formState = ref({
  classification: undefined, // 商户分类
});