docs: public static int[] subset(final int n, final int k, final Random random) {
  		requireNonNull(random, "Random");
  		if (k <= 0) {
  			throw new IllegalArgumentException(format(
  				"Subset size smaller or equal zero: %s", k
  			));
  		}
  		if (n < k) {
  			throw new IllegalArgumentException(format(
  				"n smaller than k: %s < %s.", n, k
  			));
  		}
  
  		final int[] sub = new int[k];
  		subset(n, sub,random);
  		return sub;
  	}