Steps to reproduce

• create a group called "foo".
• create a space called "bar".
• give the group "foo" space permissions to view all pages.
• delete the group "foo" without removing it from space permissions.
• call the rest api "/rest/api/space/bar?expand=permissions" with a "GET" request

What happens
In the permissions array you will still find the group "foo".

What should happen
In permissions array, group "foo" shouldn't exist anymore.