"expo start --web" suddenly failing with "Body must be a string. Received: undefined" - react-native

Question

I have just recently started with React Native and expo.
After completing a test app in the local web/dev server, I have been able to get it to work on an Android phone over a USB connection. But now the previously working web/dev server is failing:
> expo start --web
Starting project at C:\...\testproject
Body must be a string. Received: undefined.
Error: Body must be a string. Received: undefined.
at devAssert (C:\...\testproject\node_modules\graphql\jsutils\devAssert.js:12:11)
at new Source (C:\...\testproject\node_modules\graphql\language\source.js:37:56)
at new Parser (C:\...\testproject\node_modules\graphql\language\parser.js:86:62)
at Object.parse (C:\...\testproject\node_modules\graphql\language\parser.js:30:16)
at Object.<anonymous> (C:\...\testproject\node_modules\graphql-tools\src\stitching\introspectSchema.ts:7:48)
at Module._compile (internal/modules/cjs/loader.js:1085:14)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:1114:10)
at Module.load (internal/modules/cjs/loader.js:950:32)
at Function.Module._load (internal/modules/cjs/loader.js:790:12)
at Module.require (internal/modules/cjs/loader.js:974:19)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! testproject#1.0.0 dev:web: `expo start --web`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the testproject#1.0.0 dev:web script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
The expo build:web command is still working though. It exports a fully functional web app to the web-build directory.
Dependencies:
"dependencies": {
"expo": "^45.0.6",
"expo-gl": "^11.3.0",
"expo-keep-awake": "^10.1.1",
"expo-navigation-bar": "^1.2.0",
"expo-splash-screen": "~0.15.1",
"expo-status-bar": "^1.3.0",
"expo-three": "^6.1.0",
"expo-web-browser": "~10.2.1",
"react": "17.0.2",
"react-dom": "^18.2.0",
"react-native": "0.68.2",
"react-native-safe-area-context": "^4.3.1",
"react-native-screens": "^3.13.1",
"react-native-web": "^0.18.1",
"three": "^0.141.0"
},
"devDependencies": {
"#babel/core": "^7.18.5",
"#expo/webpack-config": "^0.16.24",
"#types/babel__core": "^7.1.19",
"#types/babel__template": "^7.4.1",
"#types/react": "~18.0.14",
"#types/react-native": "^0.69.0",
"#types/three": "^0.141.0",
"#typescript-eslint/eslint-plugin": "^5.29.0",
"#typescript-eslint/parser": "^5.29.0",
"eas-cli": "^0.54.1",
"eslint": "^8.18.0",
"eslint-config-prettier": "^8.5.0",
"eslint-plugin-react": "^7.30.1",
"eslint-plugin-react-hooks": "^4.6.0",
"expo-cli": "^5.4.11",
"expo-dev-client": "^1.0.0",
"husky": "^8.0.0",
"prettier": "^2.7.1",
"typescript": "~4.7.4"
}

Answer 1

Problem solved.
expo start -c -w (with -c to clear the cache) revealed the problem.
Apparently a dependency update had gone wrong; React is at 17, and React-DOM and the types are at 18. Upgrading all to 18 resulted in new/different errors, so I have now downgraded all to 17 and the dev server is working again.

Answer 2

for me, I had expo-cli as a dependency, as soon as I removed this, the message went away

Answer 3

I had expo-cli(v5.4.7) as a dev dependency. Upgrading to v6.0.6 made it work for me