code: public static <E, C extends Counter<E>> C saferL2Normalize(C c) {
      return scale(c, 1.0 / saferL2Norm(c));
    }
docs: L2 normalize a counter, using the "safer" L2 normalizer.
  
  @param c
  The {@link Counter} to be L2 normalized. This counter is not
  modified.
  @return A new l2-normalized Counter based on c.