code: public static <T> KeyRange<T> atMostBackward(final T stop) {
      return new KeyRange<>(KeyRangeType.BACKWARD_AT_MOST, null, stop);
    }
docs: Create a {@link KeyRangeType#BACKWARD_AT_MOST} range.
  
  @param <T>  buffer type
  @param stop stop key (required)
  @return a key range (never null)