I've answered to Chris my whole life. I do object gently to Christy, a diminutive sometimes used by people of Irish or Maori extraction, because it is to me the diminutive of Christine, not Christopher. My pal Mr. Robinson answers to Jack or John. My wife prefers that we call her Judy, not Judith, and she knows and does not object to being called Her Indoors on this site. My son answers to Matt, Matty, or Math without thinking about it.

I can't see the problem, provided there is no malice involved. It was normal in my childhood for a popular person to be given a diminutive, the less popular being given one that might have had an insulting inference.
Even my Mudcat name Gurney is a childhood nickname, not from the wheeled stretcher but from a TV character.