code: static Integer denominator(final String s) {
          if ("".equals(s)) {
              return null;
          }
          String[] tokens = s.split("/");
          return (tokens.length < 2) ? null : emptyToNullInteger(tokens[1]);
      }
docs: Parse the specified string as a fraction and return the denominator, if any.
  
  @param s string to parse
  @return the denominator from the specified string parsed as a fraction,
  or null if the string is empty or if the fraction has no denominator