ual-anchor | Identity and session through ESR | Authentication library

I am making an NPC path tool in Unity and I have borrowed some functionality from this other post on stack overflow (How to make individual anchor points of bezier continuous or non-continuous).

I have not copied or repurposed anything that I could not have made myself, with the only exception being this line (at the bottom of the post), that unfortunately the entire program is dependent upon.

I understand that this is some kind of inline function declaration/definition, but I do not understand how it works. I think that the end result is a list of ControlPoint's being generated but I am not entirely sure.

I would not be that bothered but I am constantly getting an index out of bounds error from a loop in another class and the error code is pointing to this line. I am sure that I would be able to solve it if I could understand this line and deconstruct it. I suspect that it's some kind of C# specific ternary operator but I've never seen it before and although I've tried, I have no idea what to google or where to find the appropriate documentation to explain it.

So in essence I am asking for an explanation of the syntactic sugar on this specific line of code that this person has used so that I am able to deconstruct this line of code and fix the issue in my program.

Any help is appreciated, cheers!

(Original code sample):