The problem is in the upstream of your code. If you bake the cuves out of the Join Curves component then explode them, you will see a duplicate curve. When you join same curves together, they become closed curve.
The order “0” and “2” are the same curve in that list. Why did you list the same curve and join them together?
Aaah… I want to make an arch as an output, out of a gap between two circles. And the case is when the gap between the circles is 0. So normally there would be 3 items in the list…
In this case, I think an operation like this would be necessary.