diff --git a/src/core/util/core.js b/src/core/util/core.js
index 827b79c60..be8c2fa4d 100644
--- a/src/core/util/core.js
+++ b/src/core/util/core.js
@@ -10,11 +10,8 @@ export function cached(fn) {
   const cache = Object.create(null);
   return function (str) {
     const key = isPrimitive(str) ? str : JSON.stringify(str);
-    if (key in cache) {
-      return cache[key];
-    }
-
-    return (cache[key] = fn(str));
+    const hit = cache[key];
+    return hit !== undefined ? hit : (cache[key] = fn(str));
   };
 }