TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received type undefined

[dancesWithCycles]

Hi folks,
I hope you are well and I thank you very much for making the project. I am trying to get it on the road but failed so far. This is what I did yet.

1. I checked out the git repository: 'git clone <>'.
2. I installed dependencies: 'npm install'.
3. I launched the app: 'npm start'.

What I receive as answer text in the web browser is the following:

'
TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received type undefined
at validateString (internal/validators.js:125:11)
at Object.join (path.js:1147:7)
at noopServiceWorkerMiddleware (/home/user/GitHub/react-leaflet-demo/node_modules/react-dev-utils/noopServiceWorkerMiddleware.js:14:26)
at Layer.handle [as handle_request] (/home/user/GitHub/react-leaflet-demo/node_modules/express/lib/router/layer.js:95:5)
at trim_prefix (/home/user/GitHub/react-leaflet-demo/node_modules/express/lib/router/index.js:317:13)
at /home/user/GitHub/react-leaflet-demo/node_modules/express/lib/router/index.js:284:7
at Function.process_params (/home/user/GitHub/react-leaflet-demo/node_modules/express/lib/router/index.js:335:12)
at next (/home/user/GitHub/react-leaflet-demo/node_modules/express/lib/router/index.js:275:10)
at launchEditorMiddleware (/home/user/GitHub/react-leaflet-demo/node_modules/react-dev-utils/errorOverlayMiddleware.js:20:7)
at Layer.handle [as handle_request] (/home/user/GitHub/react-leaflet-demo/node_modules/express/lib/router/layer.js:95:5)
at trim_prefix (/home/user/GitHub/react-leaflet-demo/node_modules/express/lib/router/index.js:317:13)
at /home/user/GitHub/react-leaflet-demo/node_modules/express/lib/router/index.js:284:7
at Function.process_params (/home/user/GitHub/react-leaflet-demo/node_modules/express/lib/router/index.js:335:12)
at next (/home/user/GitHub/react-leaflet-demo/node_modules/express/lib/router/index.js:275:10)
at handleWebpackInternalMiddleware (/home/user/GitHub/react-leaflet-demo/node_modules/react-dev-utils/evalSourceMapMiddleware.js:42:7)
at Layer.handle [as handle_request] (/home/user/GitHub/react-leaflet-demo/node_modules/express/lib/router/layer.js:95:5)

'
Who has an idea what goes wrong here?

Cheers!