Return an Attribute object instead of an array

Might be a relict from before Drupal 8.3? https://www.drupal.org/node/2818293 →

@larowlan, what do you think?
And should we postpone this on 📌 Remove the special handling of 'class' attribute in favour of classed plugins Needs work ?

@Anybody I think your issue lies elsewhere.

This module doesn't do anything for outputting the attributes.

It provides a widget only.

The formatter is provided by core and the output happens in \Drupal\Core\Render\Element\Link::preRenderLink

Thank you very much @larowlan for your super fast and clear reply. I'm sorry I didn't see that myself.
So I guess this must be caused by a further module enabled. I'll debug that, thanks and sorry for taking your time.

@Anybody no problem at all mate, always got time for those who pitch in. Have really appreciated all your work in the module's queue.