Vue&Pug使用，自定义指令解析错误

Question

<template>  div(v-drag) 如上代码，如果v-drag指令不传值，pug会解析成v-drag="v-drag",会抛出错误:[Vue warn]: Property or method "v" is not defined on the instance but referenced during render为了不让他报错，你必须赋个空置，如v-drag='',该如何让他正确解析为v-drag