diff --git a/src/registries/npm-registry.js b/src/registries/npm-registry.js
index 8e711d0db3..5fc7dab25a 100644
--- a/src/registries/npm-registry.js
+++ b/src/registries/npm-registry.js
@@ -177,7 +177,7 @@ export default class NpmRegistry extends Registry {
       }
     }
 
-    return '';
+    return undefined;
   }
 
   getScopedOption(scope: string, option: string): mixed {