I think it's very sweet, recognizable but not overused, and would be cute on a child but would grow into adulthood well.
Bernie is an obvious nn, but I don't care for it much. You might be able to get away with Beri ("berry"),
Nadine,
Nadia,
Addie,
Ada,
Ettie, or
Etta. In the movie "Circle of Friends" I believe
Bernadette was
Minnie Driver's character's name was
Bernadette and she went by
Bennie. That's very cute too. :b