Since its a divalent cation, aren't the 2 electrons from 4S lost, not promoted?
This one messed with my head but I think the electronic config of Nickel is [Ar]4s2 3d8
and transition metal cations lose from the highest n level which is 4s making Ni(II) [Ar]3d8
If it were trivalent, (I don't think Nickel has that redox state though), then it goes down to 3d7