uniapp表单校验报错form.value.validate is not a function

       1.定义表单校验规则

// 表单验证规则
const rules = ref({
  username: {
    rules: [
      { required: true, errorMessage: '请输入用户名' }
    ]
  },
  password: {
    rules: [
      { required: true, errorMessage: '请输入密码' }
    ]
  }
});

// 表单引用
const form = ref(null);

         2.调用校验方法

const handleLogin = async () => {
  try {
    // 验证表单
    const valid= await form.value?.validate?.()
	
	uni.request({
		url: baseUrl + '/user/login',
		success: (res) => {
			console.log(res.data)
		}
	})
    uni.showToast({
      title: '登录成功',
      icon: 'success'
    });

  } catch (err) {
    console.log('表单错误信息：', err);
  }
};