diff --git a/app/Classes/Modules/Transactions/DataTransferObjects/TransactionObject.php b/app/Classes/Modules/Transactions/DataTransferObjects/TransactionObject.php
index 780615a0..6b097b9e 100644
--- a/app/Classes/Modules/Transactions/DataTransferObjects/TransactionObject.php
+++ b/app/Classes/Modules/Transactions/DataTransferObjects/TransactionObject.php
@@ -231,7 +231,10 @@ class TransactionObject implements DataTransferObject
         }, $this->details);
     }
 
-    public function getPaymentReference(): string
+    /**
+     * @return string|null
+     */
+    public function getPaymentReference(): ?string
     {
         return $this->paymentReference;
     }