Pilou,

The 3 colours of wires and connectors (inputs & outputs) represents the 3 data types:
GREEN = number data (numbers or numArrays)
PINK = point data (points or pointArrays)
YELLOW = objects (curves, surfaces or bReps)

So Curve & polyline nodes inputs are PINK and hence point arrays (minimum length of 2)

Hope this makes sense.
James
https://www.instagram.com/nodeology/

PS Keep up the good work.