code: public static Slug valueOf(final String value) {
          if (value != null) {
              final String decoded = decodeSlug(value);
              if (decoded != null) {
                  return new Slug(decoded);
              }
          }
          return null;
      }
docs: Get a Slug object from a decoded string value.
  @param value the raw value of the HTTP header, may be null
  @return a Slug object with a decoded value or null