diff --git a/packages/form/src/Form.php b/packages/form/src/Form.php
index 8cd27cccd..110686a3e 100644
--- a/packages/form/src/Form.php
+++ b/packages/form/src/Form.php
@@ -142,7 +142,7 @@ public function add(string $name, mixed $field, ?string $fieldset = null): Abstr
         $field->setName($name);
 
         $namespace = implode('/', $this->namespaceStack) . '/' . $namespace;
-        $namespace = trim($namespace, '/') ?: null;
+        $namespace = trim($namespace, '/') ?: '';
 
         return $this->addField($field, $fieldset, $namespace);
     }