diff --git a/app/Entities/Equipment/ServerPartEntity.php b/app/Entities/Equipment/ServerPartEntity.php
index 66ef6fe..6c42a8c 100644
--- a/app/Entities/Equipment/ServerPartEntity.php
+++ b/app/Entities/Equipment/ServerPartEntity.php
@@ -37,7 +37,7 @@ class ServerPartEntity extends EquipmentEntity
     {
         return $this->attributes['billing'];
     }
-    public function getBillingAt(): string
+    public function getBillingAt(): ?string
     {
         return $this->attributes['billing_at'];
     }