I'm in a react project that runs perfectly with no errors or warning when using yarn start, but when I try yarn build I get the following error in my console:

Cannot read property 'toLowerCase' of undefined
CompileError: Begins at CSS selector .m-n1

I have already searched in my code and there's no ".m-n1" class or something like this in any component or scss.

Here it is my package.json file

  "name": "removedForThisPost",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "@clayui/alert": "^3.40.0",
    "@clayui/card": "^3.41.0",
    "@clayui/core": "^3.41.0",
    "@clayui/css": "^3.41.0",
    "@clayui/drop-down": "^3.41.0",
    "@clayui/empty-state": "^3.40.0",
    "@clayui/form": "^3.40.0",
    "@clayui/icon": "^3.40.0",
    "@testing-library/jest-dom": "^5.11.4",
    "@testing-library/react": "^11.1.0",
    "@testing-library/user-event": "^12.1.10",
    "@types/jest": "^26.0.15",
    "@types/node": "^12.0.0",
    "@types/react": "^17.0.0",
    "@types/react-dom": "^17.0.0",
    "axios": "^0.24.0",
    "react": "^17.0.2",
    "react-dom": "^17.0.2",
    "react-scripts": "4.0.3",
    "sass": "^1.45.0",
    "timeago.js": "^4.0.2",
    "typescript": "^4.1.6",
    "web-vitals": "^1.0.1"
  },
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },
  "eslintConfig": {
    "extends": [
      "react-app",
      "react-app/jest"
    ]
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  }
}

Extra information: I'm using NVM for node versions and at this moment I'm at Node 14.18.2 (npm v6.14.15)!

If you guys need any other information let me know!

CodePudding user response：

okay, I found for the exact same issue that u were dealingwith, here is a solution for you npm run build - Failed to compile - Cannot read property 'toLowerCase' of undefined To summarize this, you got a problem with a missing value in your code. also, try to search in your code with ctrl shift f command ".m-n1"

CodePudding user response：

Just in case:

Have you search in your project the term "m-n1" as well? (I mean just "m-n1", without beginning it in period/dot).

If you didn't, try again and you will probably find a css file which will have some kind of error in the code (a missing attribute separator sign, a typo, ...).