From a5dd2903058f15e416f9695866d331ab7a0a100b Mon Sep 17 00:00:00 2001
From: mohawk2 <mohawk2@users.noreply.github.com>
Date: Sun, 21 Jan 2018 02:54:53 +0000
Subject: [PATCH] More accurate check for cache-hit in memoize3

`WeakMap.get` returns `undefined` on cache miss. Checking for false instead of `undefined` will give a false cache-miss and recalculate when a false value is returned by the memoised function.
---
 src/jsutils/memoize3.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/jsutils/memoize3.js b/src/jsutils/memoize3.js
index 95b27c7b2b..18d938fb53 100644
--- a/src/jsutils/memoize3.js
+++ b/src/jsutils/memoize3.js
@@ -24,7 +24,7 @@ export default function memoize3<T: (a1: any, a2: any, a3: any) => any>(
       cache2 = cache1.get(a2);
       if (cache2) {
         const cachedValue = cache2.get(a3);
-        if (cachedValue) {
+        if (cachedValue !== undefined) {
           return cachedValue;
         }
       }