next build failed with firebase-admin

[mikan3rd]

I want to use getServerSideProps with firestore, so I added firebase-admin.

It had no problem when next dev, but I could not do next build.

The error is like this

> Build error occurred
Error: error reading first path in the walk /protos
Error: ENOENT: no such file or directory, lstat '/protos'
    at EventEmitter.<anonymous> (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:89524:28)
    at Object.onceWrapper (events.js:422:26)
    at EventEmitter.emit (events.js:315:20)
    at fn (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:89359:17)
    at statter (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:89396:7)
    at walkdir (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:89528:3)
    at Function.module.exports.Ftcu.walkdir.sync (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:89274:10)
    at Object.<anonymous> (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:164967:6)
    at Object.b1/w (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:165211:30)
    at __webpack_require__ (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:23:31)
    at Object.qLMp (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:228240:16)
    at __webpack_require__ (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:23:31)
    at Object.c0x5 (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:169363:22)
    at __webpack_require__ (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:23:31)
    at FirebaseNamespace.get [as firestore] (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:276997:29)
    at Module.jIS5 (/Users/mikan3rd/practice/commitly-next-web/.next/serverless/pages/profile/[username].js:203713:27)
error Command failed with exit code 1.

In detail, Please check this PR and Github Actions result
mikan3rd/commitly#60

(Oddly enough, the build has been successful on the vercel where I'm hosting it.)

I need your help!

[mikan3rd]

The problem seems to have been caused by declaring admin.firestore().collection() globally.

I modified it to declare the above in the function, and the build succeeds.