Incorrect type hint in rdf_sync_entity_bundle_field_info() hook implementation

What I read in the link that you've mentioned (this one: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Entity%21...) is that this hook provides field definitions for a specific bundle within an entity type. And the parameter's documentation is string $bundle: The bundle., not leaving the option for it to be NULL.

I was looking to the code that dispatches this hook, and I can see $bundle is ALWAYS non-NULL. I agree with @dxvargas but let's keep it open for a while.