code: public static final Set<String> fromCommaSeparatedValues(String csv) {
          if (csv == null || csv.isEmpty()) {
              return Collections.EMPTY_SET;
          }
          String[] tokens = csv.split(",");
          return new HashSet<String>(Arrays.asList(tokens));
      }
docs: Given a comma-separated list of values, return a set of those values.
  If the passed string is null, the EMPTY_SET is returned.
  If the passed string is empty, the EMPTY_SET is returned.