code: public T getQuantileLowerBound(final double fraction) {
      return getQuantile(max(0, fraction - Util.getNormalizedRankError(k_, false)));
    }
docs: Gets the lower bound of the value interval in which the true quantile of the given rank
  exists with a confidence of at least 99%.
  @param fraction the given normalized rank as a fraction
  @return the lower bound of the value interval in which the true quantile of the given rank
  exists with a confidence of at least 99%. Returns NaN if the sketch is empty.