code: @SuppressWarnings("unchecked")
      public static <T> IntervalCollection<T> on(TimeLine<T> timeLine) {
  
          if (timeLine.equals(PlainDate.axis())) {
              return (IntervalCollection<T>) onDateAxis();
          } else if (timeLine.equals(PlainTime.axis())) {
              return (IntervalCollection<T>) onClockAxis();
          } else if (timeLine.equals(PlainTimestamp.axis())) {
              return (IntervalCollection<T>) onTimestampAxis();
          } else if (timeLine.equals(Moment.axis())) {
              return (IntervalCollection<T>) onMomentAxis();
          }
  
          return new GenericWindows<>(timeLine, Collections.emptyList());
  
      }
docs: /*[deutsch]
  <p>Liefert eine leere Instanz f&uuml;r Intervalle auf dem angegebenen Zeitstrahl. </p>
  
  @return  empty generic {@code IntervalCollection}
  @see     net.time4j.engine.TimeAxis
  @see     net.time4j.engine.CalendarFamily#getTimeLine(String)
  @see     net.time4j.engine.CalendarFamily#getTimeLine(net.time4j.engine.VariantSource)
  @see     CalendarYear#timeline()
  @see     CalendarQuarter#timeline()
  @see     CalendarMonth#timeline()
  @see     CalendarWeek#timeline()
  @since   5.0