code: public static <R extends Comparable, C extends Comparable, V> TreeBasedTable<R, C, V> create() {
      return new TreeBasedTable<>(Ordering.natural(), Ordering.natural());
    }
docs: Creates an empty {@code TreeBasedTable} that uses the natural orderings of both row and column
  keys.
  
  <p>The method signature specifies {@code R extends Comparable} with a raw {@link Comparable},
  instead of {@code R extends Comparable<? super R>}, and the same for {@code C}. That's
  necessary to support classes defined without generics.