RadioButton

[JoanZapata]

You're RadioButton isn't a subclass of the GWT RadioButton nor a proper delegator.
I can't get the current state of the button, there is no getValue() method.

https://github.com/nyao/bootstrap4gwt/blob/master/src/com/github/nyao/bootstrap4gwt/client/ui/RadioButton.java

Maybe you should give access to the underlying GWT widget when you're not subclassing it, or add delegation methods.

It's currently unusable IMO.