code: @NotNull
      public final DayOpeningHours add(@NotNull final HourRanges other) {
          Contract.requireArgNotNull("other", other);
          final HourRanges added = this.hourRanges.add(other);
          return new DayOpeningHours(dayOfTheWeek, added);
      }
docs: Adds some hour ranges to this instance and returns a new one.<br>
  <br>
  It is only allowed to call this method if the hour ranges represents only one day. This means a value like '18:00-03:00' will lead to
  an error. To avoid this, call the {@link #normalize()} function before this one and pass the result per day as an argument to this
  method.
  
  @param other
  Ranges to add.
  
  @return New instance with added times.