Checkbox click clears content or throws

[alexvcasillas]

Hello, I'm filling this issue because I'm trying to implement this library into draftjs but I'm having some issues:

1. Clicking on the checkbox to toggle its state makes the block dissapear.
   1.1. If there's other content than the checkbox block, it will throw with the following error Cannot read property 'mergeIn' of undefined.
2. When in a checkbox list, if I press "Enter" the next line won't be a checkbox, but a regular block type 🤔

I have a fully working codesandbox (which I'm currently trying to make this work 😄 ) example here which will be helpful in order to check the errors.

Regards,
Alex.