Steps to reproduce:
- Go to http://localhost:8080/xwiki/bin/view/WorkspaceManager/Install and install the Wiki template
- Create a new subwiki: Add -> Wiki
- Click "Log-Out"
- Hover over XWiki and click on Wiki Directory
- Click on the subwiki you previously created
- Click "Log-In"
- Type in your credentials and click "Log-In"
I've attached my stacktrace.