LONDON (Reuters) - Rafa Nadal may appear an unlikely traditionalist given the way he has ripped up the tennis blueprint in the past 15 years but some aspects of the sport, he believes, should not change.Fans are not the only thing missing from this year’s ATP Finals which is being held in London for the 12th and last time. Changes forced by the COVID-19 pandemic also include the absence of line judges -- with Hawkeye line-calling technology automatically deciding whether a ball is in or out. Nadal is not one to argue the toss with officials, but even if he was, there would be nobody to vent his anger at. With no room for human error, players have also been denied the chance for Hawkeye challenges -- a popular feature for tennis since it was introduced at the 2006 U.S. Open.