I have a late 2012 Mac Mini, whose compatibility with Sierra I have verified. The Mac Mini is currently on OS X El Capitan. I am trying to update it to Sierra and when I get to the step of selecting the destination disk, I get a popup that says:
"macOS Sierra supports macOS Server version 5.2. To upgrade your server data you will first need to install OS X 10.10 or 10.11 and OS X Server version 4 or 5."
There is no Server app installed in the machine. Maybe it was installed before my time under another account and then uninstalled.
What can I do to upgrade to Sierra without having to install the Server app? I have to upgrade to install the latest Xcode etc.