From 7a0edd14026bdc0507ae24896b17cfcfbccf43b7 Mon Sep 17 00:00:00 2001
From: Matthew Butterick <mb@mbtype.com>
Date: Sun, 2 Jul 2017 19:54:20 -0700
Subject: [PATCH] doublenit

---
 pitfall/restructure/struct.rkt | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pitfall/restructure/struct.rkt b/pitfall/restructure/struct.rkt
index 44343ea3..20a2fa31 100644
--- a/pitfall/restructure/struct.rkt
+++ b/pitfall/restructure/struct.rkt
@@ -91,7 +91,8 @@ https://github.com/mbutterick/restructure/blob/master/src/Struct.coffee
     (define ctx (mhasheq 'parent parent
                          'val val
                          'pointerSize 0))
-    (+ (for/sum ([(key type) (in-dict fields)])
+    (+ (for/sum ([(key type) (in-dict fields)]
+                 #:when val)
          (send type size (ref val key) ctx))
        (if include-pointers (· ctx pointerSize) 0)))