Why does car location go to (NaN,NaN,0)?

[kmamor]

My car is given a starting location of one of the intersections:

create car number: 1 {
			ask car{
			location <- one_of(intersection).location;
}

Then it is given a random target:

species car skills: [driving] {
	....
	init {...		
		}				
			
	reflex time_to_go when: final_target = nil{
			do compute_path (graph: road_network, target: one_of(intersection));
			}
		reflex move when: final_target != nil {
		do drive;
			}}

However as I start to click through the steps its location becomes (NaN,NaN,0) . NaN I understand means 'not a number'.

What might cause this to happen?