Illegal relative path with null node

If the user and/or group only get rights to acces a workspace, teh workspace and files are not shown.
There is an error in server.log "Illegal relative path with null node"
By giving the user access to domain, too, it works

1) Create an workspace
2) Give user read-only access to workspace
3) user has no rights to access the domain
=> error occurs when user logs in

1) Create workspace
2) Give user read-only access to workspace
3) Give user read-only access to domain
=> no error occurs