diff --git a/lib/models/base.js b/lib/models/base.js
index 7625ee5a8..e94e121cb 100644
--- a/lib/models/base.js
+++ b/lib/models/base.js
@@ -13,6 +13,7 @@ class Base {
   }
 
   /**
+   * @param {string} [key] A key to retrieve from the JSON object.
    * @returns {any}
    */
   json(key) {