code: public Set<Weekday> getSet() {
  
      if (this.set == null) {
        HashSet<Weekday> hashSet = new HashSet<Weekday>();
        int value = getValue().intValue();
        for (Weekday weekday : Weekday.values()) {
          int mask = (1 << weekday.ordinal());
          if ((value & mask) != 0) {
            hashSet.add(weekday);
          }
        }
        this.set = Collections.unmodifiableSet(hashSet);
      }
      return this.set;
    }
docs: This method gets an {@link Collections#unmodifiableSet(Set) unmodifiable} {@link Set} representing this
  {@link WeekdaySet}.
  
  @return the {@link Set} with all {@link Weekday}s.