code: @Override
      public DateCalculator<LocalDate> setWorkingWeek(final WorkingWeek week) {
          if (week instanceof Jdk8WorkingWeek) {
              workingWeek = (Jdk8WorkingWeek) week;
              return this;
          }
          throw new IllegalArgumentException("Please give an instance of JodaWorkingWeek");
      }
docs: Set the working week.
  @param week the JodaWorkingWeek
  @throws IllegalArgumentException if the week is not a JodaWorkingWeek.