diff --git a/src/RequestDetails.php b/src/RequestDetails.php
index e2af025..5b40999 100644
--- a/src/RequestDetails.php
+++ b/src/RequestDetails.php
@@ -60,7 +60,7 @@ public function getStatusCode(): int
      */
     public function getUserAgent(): string
     {
-        return $this->request->header('User-Agent');
+        return $this->request->header('User-Agent', 'unknown');
     }
 
     /**