diff --git a/src/CartConditions/Coupon.php b/src/CartConditions/Coupon.php
index baaae1c..e89cf2f 100644
--- a/src/CartConditions/Coupon.php
+++ b/src/CartConditions/Coupon.php
@@ -22,7 +22,7 @@ class Coupon extends CartCondition
 
     public ?int $priority = 200;
 
-    protected static ?CouponModel $couponModel;
+    protected static ?CouponModel $couponModel = null;
 
     protected static $applicableItems;