elementplus 提交表单报formEl.validate is not a function

<el-form> 元素上没有使用 ref 绑定啊，自然就没有表单实例了

官方示例如下

<template>
  <el-form
    ref="ruleFormRef"
    :model="ruleForm"
    :rules="rules"
    label-width="120px"
    class="demo-ruleForm"
    :size="formSize"
    status-icon
  >
    <el-form-item>
      <el-button type="primary" @click="submitForm(ruleFormRef)">
        Create
      </el-button>
      <el-button @click="resetForm(ruleFormRef)">Reset</el-button>
    </el-form-item>
  </el-form>
</template>

<script lang="ts" setup>
import { reactive, ref } from 'vue'
import type { FormInstance, FormRules } from 'element-plus'

const formSize = ref('default')
const ruleFormRef = ref<FormInstance>()


const submitForm = async (formEl: FormInstance | undefined) => {
  if (!formEl) return
  await formEl.validate((valid, fields) => {
    if (valid) {
      console.log('submit!')
    } else {
      console.log('error submit!', fields)
    }
  })
}
</script>