fix

quad/quadwriter/core.rkt

@@ -329,12 +329,15 @@
 (define (do-keep-with-next! reversed-lines)
   ;; paints nobreak onto spacers that follow keep-with-next lines
   ;; (we are iterating backward, so the geometrically previous ln follows the spacer)
+  (cond
+    [(null? reversed-lines) null]
+    [else
      (for ([this-ln (in-list reversed-lines)]
            [prev-ln (in-list (cdr reversed-lines))]
            #:when (and (line-spacer? this-ln)
                        (quad-ref prev-ln 'keep-with-next)))
        (make-nobreak! prev-ln)
-    (make-nobreak! this-ln)))
+       (make-nobreak! this-ln))]))
 
 (define (apply-keeps lines)
   (define groups-of-lines (contiguous-group-by (λ (x) (quad-ref x 'display)) lines))