diff --git a/src/Symfony/Component/Config/Resource/ReflectionClassResource.php b/src/Symfony/Component/Config/Resource/ReflectionClassResource.php
index 0ece672216390..f05042f8d32fa 100644
--- a/src/Symfony/Component/Config/Resource/ReflectionClassResource.php
+++ b/src/Symfony/Component/Config/Resource/ReflectionClassResource.php
@@ -140,7 +140,7 @@ private function generateSignature(\ReflectionClass $class)
 
             foreach ($class->getProperties(\ReflectionProperty::IS_PUBLIC | \ReflectionProperty::IS_PROTECTED) as $p) {
                 yield $p->getDocComment().$p;
-                yield print_r($defaults[$p->name] ?? null, true);
+                yield print_r(isset($defaults[$p->name]) ? $defaults[$p->name] : null, true);
             }
         }