If you try and submit an invalid dataset (e.g. less than 1 item per class) then the POST endpoint /datasets/create will return an HTTP400 error.

The error message in this response should be displayed on screen, but instead a React error occurs:

editor.js:240 POST http://localhost:8080/datasets/create 400 (BAD REQUEST)
Uncaught Error: Objects are not valid as a React child (found: object with keys {error, success}). If you meant to render a collection of children, use an array instead or wrap the object using createFragment(object) from the React add-ons.