With unconnected pins, I was seeing DRC errors to unconnected pins as they are assigned to the Default class and I have spacing rules to the Default class, which I use for standard low-voltage stuff.
I could have put all the Default nets in another class, but that seemed problematic as some of the nets are named, and some are not.
I could have also run named nets to the unconnected pins, but that is confusing as it might appear that the pin is used and connected to some other named net.
I then noticed that the unconnected pins are named something like unconnected-(J4-Pad3), so it was simple to create another net class named UNCONNECTED, and then assign *unconnected* nets to this class:
Since the UNCONNECTED class is not used in the DRC rules, there are no violations now.
Netclass wildcards are great!