From 84b8382a535f89df1a4a0d1272a51e8c5a464f5e Mon Sep 17 00:00:00 2001
From: Honza Machala <jan.machala@bileto.com>
Date: Wed, 10 May 2017 11:33:56 +0200
Subject: [PATCH] Added strict return types to string|null

---
 src/Message/PaymentResponse.php | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/Message/PaymentResponse.php b/src/Message/PaymentResponse.php
index 2fbaa0d..0c5965e 100644
--- a/src/Message/PaymentResponse.php
+++ b/src/Message/PaymentResponse.php
@@ -13,9 +13,10 @@ public function getAuthCode()
 
     public function getTransactionReference()
     {
-        if (isset($this->data['payId'])) {
-            return $this->data['payId'];
+        if (isset($this->data['payId']) && !empty($this->data['payId'])) {
+            return (string) $this->data['payId'];
         }
+        return null;
     }