code: @NotNull
      public final HourRanges add(@NotNull final HourRanges other) {
          Contract.requireArgNotNull("other", other);
          ensureSingleDayOnly("this", this);
          ensureSingleDayOnly("other", other);
  
          final BitSet thisMinutes = this.toMinutes();
          final BitSet otherMinutes = other.toMinutes();
          thisMinutes.or(otherMinutes);
  
          return HourRanges.valueOf(thisMinutes);
  
      }
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.