code: public static <E> Distribution<E> laplaceSmoothedDistribution(Counter<E> counter, int numberOfKeys) {
      return laplaceSmoothedDistribution(counter, numberOfKeys, 1.0);
    }
docs: Creates an Laplace smoothed Distribution from the given counter, ie adds one count
  to every item, including unseen ones, and divides by the total count.
  
  @return a new add-1 smoothed Distribution