How to populate attribute with last element from a list?

Hello all,

I have 1721 point features, which I am combining into a single line using LineBuilder.

Each node has a datetime stamp, and I want to populate the line with the attributes "start_date" and "end_date" drawn from the "date" attribute of the first and last point feature.

In the LineBuilder I have ticked the parameter Generate List, so I have a list with 1721 elements.

I can use the Attribute manager to create a new attribute "start_date" with a value of;

@Value(points{0}.date)

However, I fail to do the equivalent for the last element in the list.

@Value(points{-1}.date) is not accepted by the Text editor or the List Element Selection: points{}.date

I thought I might solve it by using ListElementCounter, which does create a new attribute with a value of 1721, but again the List Element Selection: does not accept an attribute value as an input.