Change block/field default to None

[loicteixeira]

Currently, the default value is an empty dict which is basically an invalid content state. Therefore, the editor should return None which clearly state the lack of content.

• Update springload/draftail package.
• Update springload/draftjs_exporter package.
• Update springload/draftail dependency for this package.
• Update springload/draftjs_exporter dependency for this package.
• Update block accordingly
• Update field accordingly (actually the field doesn't have a default value atm?)
• Remove the now useless form field and validator?

[thibaudcolas]

@loicteixeira I've done the work in Draftail (#40) and the exporter (#36) to support this, and updated those two here – will leave the Django changes to you if you have the time.

[thibaudcolas]

I have re-added a default value of {} within this project (bb4b68f) so that we can finish this later on.

Note that nothing needs to happen for the exporter, it will handle None or {} just the same.

[loicteixeira]

Sorry I didn't get time to look into this before my break.

Basically, the block use a custom form field to handle the '{}' string as empty.

Now that draftail returns None, this is not needed anymore. This can probably use the same formfield as the parent class, so there is no need for the form and validator linked above in the issue.

FWIW, it looks like DraftailTextBlock and DraftailTextField don't use the same underlying form field and this should be updated to the same (but potentially removing the overwrite on the block should do the trick).