diff --git a/src/ProcessStamp.php b/src/ProcessStamp.php
index c9fc3aa..61317e1 100644
--- a/src/ProcessStamp.php
+++ b/src/ProcessStamp.php
@@ -34,7 +34,7 @@ public function getTable() : string
      *
      * @return ProcessStamp
      */
-    public static function firstOrCreateByProcess(array $process, ?string $hash) : self
+    public static function firstOrCreateByProcess(array $process, ?string $hash = null) : self
     {
         if (empty($process['type'])) {
             $process['type'] = 'other';