instanceOf: Check that one of the names in non-empty string (graphql#1357)

IvanGoncharov · mjmahone · commit 10e80d05dcad · 2018-06-04T14:09:21.000-04:00
Fixes graphql#1356
diff --git a/src/jsutils/instanceOf.js b/src/jsutils/instanceOf.js
@@ -31,7 +31,7 @@ export default (process.env.NODE_ENV === 'production'
       if (value) {
         const valueClass = value.constructor;
         const className = constructor.name;
-        if (valueClass && valueClass.name === className) {
+        if (className && valueClass && valueClass.name === className) {
           throw new Error(
             `Cannot use ${className} "${value}" from another module or realm.
 
