Property binding is not updated with an empty array

The idea is that both, the property and getter, should give me the same value. This does not work

property var selectedTimeline: timeline.sectionsList[root.selectedTimelineIndex]
function getSelectedTimeline()
{ return timeline.sectionsList[root.selectedTimelineIndex] }

 
1. Click Add
2. Click Add
3. Click Print: Prints index for getSelectedTimeline() and Error for selectedTimeline
4. Change the Index to 1
5. Click Print: Prints both index