diff --git a/src/Traits/HasCommission.php b/src/Traits/HasCommission.php
index bfd6d28..17af068 100644
--- a/src/Traits/HasCommission.php
+++ b/src/Traits/HasCommission.php
@@ -15,7 +15,7 @@ trait HasCommission
     /**
      * @throws Exception
      */
-    public function calculate(string $column = null): CommissionCalculationResultContext|array|null
+    public function calculate(?string $column = null): CommissionCalculationResultContext|array|null
     {
         $service = new CommissionCalculatorService($this);
         $commissions = $service->getCalculableCommissions($column);