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