diff --git a/hwe/sammo/Command/BaseCommand.php b/hwe/sammo/Command/BaseCommand.php
index 5bc25663..65ead2ee 100644
--- a/hwe/sammo/Command/BaseCommand.php
+++ b/hwe/sammo/Command/BaseCommand.php
@@ -18,7 +18,7 @@ abstract class BaseCommand{
     static protected $actionName = 'CommandName';
     static public $reqArg = false;
     static protected $isLazyCalcReqTurn = false;
-    public $reason;
+    public ?string $reason;
 
     public function getCommandDetailTitle():string{
         return $this->getName();