vue-cli 3.0 执行npm run serve，启动报错

npm run serve 报以下错误

INFO  Starting development server...
 10% building 2/2 modules 0 active ERROR  TypeError: Cannot read property 'upgrade' of undefined
TypeError: Cannot read property 'upgrade' of undefined
    at Server.<anonymous> (D:\...\node_modules\webpack-dev-server\lib\Server.js:142:47)
    at Array.forEach (<anonymous>)
    at new Server (D:\...\node_modules\webpack-dev-server\lib\Server.js:141:27)
    at serve (D:\...\node_modules\@vue\cli-service\lib\commands\serve.js:137:20)
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:188:7)
    at Function.Module.runMain (module.js:695:11)
    at startup (bootstrap_node.js:191:16)
    at bootstrap_node.js:612:3
error Command failed with exit code 1.
info Visit https:

分析：

开始以为是node_modules出错，删了重下还是一样，发现是之前在vue.config.js中代理出问题了

devServer: {
 proxy: {
 '/api': {
   target: ''
  }
 }
}

直接像上面那样保存了，然后去跑项目，结果可想而知。