Already checked, as previously stated.
I've always liked nickel plated guns. Consequently, I've owned more than a few. I find most of the wives tales concerning the fragility of nickel to be exactly that. Hoppe's might be hazardous to the integrity of the finish, if you dump the gun into a bucket of it and leaving it soaking for an extended period of time. I don't use Hoppe's because I find it to be pretty poor at anything its supposed to do, not due to concerns over finish wear. I've also never seen an example of a yellowed nickel finish. I currently have three nickeled guns in my safe. All of them are north, or just south, of forty years old. None of them came to me new, nor have they been babied since. The only treatment they receive is an occasional wipe down with a clean cloth. I haven't treated them like fine china or kept them in hermetically sealed chambers and yet they're as nice as the day I acquired them. We tend to forget that nickel was the original hard use finish.