diff --git a/src/Bridge/NelmioApiDoc/Parser/ApiPlatformParser.php b/src/Bridge/NelmioApiDoc/Parser/ApiPlatformParser.php
index 9ff4c608c93..d5a6b9c2bb0 100644
--- a/src/Bridge/NelmioApiDoc/Parser/ApiPlatformParser.php
+++ b/src/Bridge/NelmioApiDoc/Parser/ApiPlatformParser.php
@@ -238,7 +238,7 @@ private function parseProperty(ResourceMetadata $resourceMetadata, PropertyMetad
                     return $data;
                 }
 
-                $data['subType'] = $subProperty['subType'];
+                $data['subType'] = $subProperty['subType'] ?? null;
                 if (isset($subProperty['children'])) {
                     $data['children'] = $subProperty['children'];
                 }