code: @Override
    public int compareTo(DiscordRecord other) {
      if (null == other) {
        throw new NullPointerException("Unable compare to null!");
      }
      return Double.compare(other.getNNDistance(), this.nnDistance);
    }
docs: The simple comparator based on the distance. Note that discord is "better" if the NN distance
  is greater.
  
  @param other The discord record this one is compared to.
  @return True if equals.