THE CANADIAN PRESS/AP-Matt RourkeA quick errand to Walmart turned into an overnight adventure for dozens of shoppers in southern Ontario when whiteout conditions meant they couldn't leave the store, and employees pumped up air mattresses and set up a buffet with deli food for the unexpected guests.Nickoli and her boyfriend had been en route from Ohio to Peterborough, Ont., to spend Christmas with her boyfriend's family when the worsening weather forced the closure of Highway 401.The couple booked a room in Chatham-Kent and decided to stop at Walmart on the way, but they didn't get far after shopping.The statement noted there was even an impromptu birthday celebration for one employee at midnight, complete with cake and candles."I think when we first got there, everybody was in shock and they were a little bit upset."