A wrong car you fix. Guard empty lists.

Goal

Print car of a non-empty list; skip empty.

(print (car '(Nairobi)))

(define (safe-car xs)
  (if (null? xs)
      "empty"
      (car xs)))
(print (safe-car '(Mombasa Kisumu)))
(print (safe-car '()))

(print (cdr '(Nakuru Eldoret)))

(define (need xs)
  (if (null? xs)
      (error "empty till")
      (car xs)))
(print (need '(12)))