diff --git a/src/ArrayToXml.php b/src/ArrayToXml.php
index 0053138..cf43a99 100644
--- a/src/ArrayToXml.php
+++ b/src/ArrayToXml.php
@@ -212,7 +212,7 @@ protected function addNode(DOMElement $element, string $key, mixed $value): void
     protected function addNodeTypeAttribute(DOMElement $element, mixed $value): void
     {
         if (is_null($value)) {
-            if (!$this->rootNode->hasAttribute('xmlns:xsi')) {
+            if (! $this->rootNode->hasAttribute('xmlns:xsi')) {
                 $this->rootNode->setAttribute('xmlns:xsi', 'http://www.w3.org/2001/XMLSchema-instance');
             }