Wrong value displayed for the details of the changes in emails in the global notifications administration when value is unset

How to reproduce:

• get into the situation of having no value set for the details of the changes in emails, for the global settings
  • afaict, this happens on an upgrade from a version previous to the introduction of global settings
  • otherwise, go to XWiki.Notifications.Code.NotificationAdministration and delete the XWiki.Notifications.Code.NotificationEmailPreferenceClass object or edit in object mode and set the value to "---"
• go to your own user profile
• set the detail of changes in email of your own user profile to "none"
• go to the global administration and check the value displayed for detail of changes in email

Expected result:

• the displayed value should either be — to show that it's unset or "Standard" to show what would actually apply (the default seems to be 'standard')

Actual result:

• "None" would be displayed, which is the value set for the current admin looking at the screen