Input in summerized columns from subItems when there is no subitem (eg. timeline)

Hi there,

I have started to use subitems and created a timeline column that summerize all subitems timeline. The thing is that I have some items with no sub-items and I can’t specify the timeline on this item.
Subitems timeline

Could you please enable the input on a “summerized timeline” when there is no subitem ?