Rights set to XWiki.superadmin user are not displayed in the administration

How to reproduce:

• give some rights to the XWiki.superadmin user (or xwiki:XWiki.superadmin)
  • this needs to be done either by adding an object - for example
  • or programmatically - for example, some application could do so
• go to the page's administration, in the users tab, select both global and local users if you're on a subwiki
• try to filter by superadmin or otherwise find this right

Expected result:

• the right is found and displayed and can be modified / removed

Actual result:

• the right setting is not found

Note: generally the rights administration is not showing rights given to nonexistent entities , users or groups, as such rights should not exist (cannot be given through this UI and are deleted upon entity deletion), and this can make sense (although it can also be seen as a bug). However, superadmin is an existent entity - a user can login with superadmin and have an application give them explicit rights.