diff --git a/src/Utils/ItemDetailForm.php b/src/Utils/ItemDetailForm.php
index 3ad857bf..038e2eb4 100644
--- a/src/Utils/ItemDetailForm.php
+++ b/src/Utils/ItemDetailForm.php
@@ -16,7 +16,7 @@ final class ItemDetailForm extends Container
 	private $callableSetContainer;
 
 	/** @var ?array */
-	private ?array $httpPost;
+	private ?array $httpPost = null;
 
 	/** @var array<bool> */
 	private array $containerSetByName = [];