12강, POST를 보내면 [ERR_HTTP_HEADERS_SENT] 에러

- Postman으로 email, PW를 보내며 '비밀번호가 틀렸습니다' 가 Response로 돌아오면서 아래 에러가 나옵니다... 비번은 분명 맞는데 이런 에러가 나옵니다ㅜ 혹시 이유를 알 있나요?

- 좀 길지만 전체 코드 복붙했습니다. 감사합니다! 

CODE

ERROR

_http_outgoing.js:558

    throw new ERR_HTTP_HEADERS_SENT('set');

    ^

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

    at ServerResponse.setHeader (_http_outgoing.js:558:11)

    at ServerResponse.header (/Users/user/VS Code/project_with_NodeJS/boiler-plate/node_modules/express/lib/response.js:771:10)

    at ServerResponse.send (/Users/user/VS Code/project_with_NodeJS/boiler-plate/node_modules/express/lib/response.js:170:12)

    at ServerResponse.json (/Users/user/VS Code/project_with_NodeJS/boiler-plate/node_modules/express/lib/response.js:267:15)

    at /Users/user/VS Code/project_with_NodeJS/boiler-plate/index.js:48:20

    at /Users/user/VS Code/project_with_NodeJS/boiler-plate/models/user.js:62:9

    at /Users/user/VS Code/project_with_NodeJS/boiler-plate/node_modules/bcrypt/bcrypt.js:210:13

    at processTicksAndRejections (internal/process/task_queues.js:75:11) {

  code: 'ERR_HTTP_HEADERS_SENT'

}

npm ERR! code ELIFECYCLE

npm ERR! errno 1

npm ERR! boiler-late@1.0.0 start: `node index.js`

npm ERR! Exit status 1

npm ERR! 

npm ERR! Failed at the boiler-late@1.0.0 start script.

npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:

npm ERR!     /Users/user/.npm/_logs/2020-12-28T03_02_38_926Z-debug.log