There are two issues here.
First, you really shouldn't be calling ulx.adduserid for your use case (I understand this works for a lot of people for their needs, but it was not something I designed around); instead, call
ULib.ucl.addUser. Or if you
really want to keep using the ULX command, call it from console using
RunConsoleCommand.
Second, which directly addresses your problem, you're passing nil to calling_ply which would never be nil under normal circumstances (the server console is simply an invalid entity). I haven't actually verified this is the issue, but I'm fairly confident it is.