diff --git a/src/Controller/Transaction.php b/src/Controller/Transaction.php
index a61c88080..2a46b093c 100644
--- a/src/Controller/Transaction.php
+++ b/src/Controller/Transaction.php
@@ -642,7 +642,7 @@ public function getAcceptedContentTypes(): MediaTypes
     {
         $formatQueryOption = $this->getFormat()->getValue();
 
-        if (Str::startsWith($formatQueryOption, ['json', 'xml'])) {
+        if ($formatQueryOption && Str::startsWith($formatQueryOption, ['json', 'xml'])) {
             if (!in_array($formatQueryOption, ['json', 'xml'])) {
                 throw new BadRequestException(
                     'invalid_short_format',