I believe this is a flawed logic in the application where you will be forced to create a space before the user(admin in this case) is able to access Confluence.

Steps to reproduce :

1. Install Confluence 5.4.3
2. Upgrade to Confluence 5.9.12
3. Login to Confluence as confluence administrator
4. The welcome screen will be present that force the user to create a space even though the upgraded Confluence instances already contains spaces :
   

Existing behavior : the welcome screen forces the user(admin in this case) to create a space

Expected behavior : the space creation portion should be omitted at least for upgraded instances.