diff --git a/src/Required/RequestInterface.php b/src/Required/RequestInterface.php
index 022a73c..9b4e99b 100644
--- a/src/Required/RequestInterface.php
+++ b/src/Required/RequestInterface.php
@@ -20,10 +20,10 @@ interface RequestInterface
 
     /**
      * Returns a referred user response variable.
-     * @param string $k The key the user is sending
+     * @param string $key The name of the value the user is sending
      * @return string
      */
-    public function getResp(string $key): string;
+    public function getResp(string $key): ?string;
 
 
 }