This dominant enterprise has an ongoing risk that can't be ignored.Warren Buffett's Berkshire Hathaway is known for having huge stakes in companies like Apple, Coca-Cola, and Bank of America. But the conglomerate also has much smaller positions.It has a tiny holding in Visa (V 1.29%) that most investors might not know about. Despite this being a high-quality business that Buffett owns, it's not without downside. There's one key risk facing this otherwise phenomenal stock that has climbed 403% in the past de ...