private Set<DayOfWeek> days() {
            if (start.isEmpty() || end.isEmpty()) return EnumSet.allOf(DayOfWeek.class);
            Set<DayOfWeek> days = EnumSet.noneOf(DayOfWeek.class);
            for (LocalDate date = start.get(); !date.isAfter(end.get()) && days.size() < 7; date = date.plusDays(1)) {
                days.add(date.getDayOfWeek());
            }
            return days;
        }
Return days of week found in this range
config-model-api/src/main/java/com/yahoo/config/application/api/TimeWindow.java