code: public CursorIterator<T> iterate(final Txn<T> txn, final KeyRange<T> range) {
      return iterate(txn, range, null);
    }
docs: Iterate the database in accordance with the provided {@link KeyRange} and
  default {@link Comparator}.
  
  @param txn   transaction handle (not null; not committed)
  @param range range of acceptable keys (not null)
  @return iterator (never null)