Q:

TypeERROR after yarn upgrade (ReactJS project)

I ran the command yarn upgrade and then I got this error next time I did yarn start, and I have no idea why? Hoping someone can tell me whats going on here? No idea what to do to solve it. Tried googling it, without much luck as to what is wrong. 
TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received type undefined
at validateString (internal/validators.js:113:11)
at Object.join (path.js:375:7)
at noopServiceWorkerMiddleware (C:\Users\perni\Projects\prime\node_modules\react-dev-utils\noopServiceWorkerMiddleware.js:14:26)
at Layer.handle [as handle_request] (C:\Users\perni\Projects\prime\node_modules\express\lib\router\layer.js:95:5)
at trim_prefix (C:\Users\perni\Projects\prime\node_modules\express\lib\router\index.js:317:13)
at C:\Users\perni\Projects\prime\node_modules\express\lib\router\index.js:284:7
at Function.process_params (C:\Users\perni\Projects\prime\node_modules\express\lib\router\index.js:335:12)
at next (C:\Users\perni\Projects\prime\node_modules\express\lib\router\index.js:275:10)
at launchEditorMiddleware (C:\Users\perni\Projects\prime\node_modules\react-dev-utils\errorOverlayMiddleware.js:20:7)
at Layer.handle [as handle_request] (C:\Users\perni\Projects\prime\node_modules\express\lib\router\layer.js:95:5)
at trim_prefix (C:\Users\perni\Projects\prime\node_modules\express\lib\router\index.js:317:13)
at C:\Users\perni\Projects\prime\node_modules\express\lib\router\index.js:284:7
at Function.process_params (C:\Users\perni\Projects\prime\node_modules\express\lib\router\index.js:335:12)
at next (C:\Users\perni\Projects\prime\node_modules\express\lib\router\index.js:275:10)
at handleWebpackInternalMiddleware (C:\Users\perni\Projects\prime\node_modules\react-dev-utils\evalSourceMapMiddleware.js:42:7)
at Layer.handle [as handle_request] (C:\Users\perni\Projects\prime\node_modules\express\lib\router\layer.js:95:5)

A:

Try running yarn cache list to print out your cached packages, then you can compare with the version in your package.json to make sure they match.
If you still get errors, run yarn cache clean to clear your entire cache and run yarn install to repopulate them.

