Since the `isPristine` value got set to `true` every time the field was empty, the Next button usually got correctly disabled, but no error was rendered.

Currently the `isPristine` doesn't get re-set when input is deleted, meaning there can be a green check mark when the value is not required, but if it is required, the error message gets rendered properly. I believe lingering green checkmark will be much less confusing for the user than disabled Next buttons without any indication of error.