diff --git a/src/ArrayToXml.php b/src/ArrayToXml.php
index 8eba571..4a0a457 100644
--- a/src/ArrayToXml.php
+++ b/src/ArrayToXml.php
@@ -241,7 +241,7 @@ protected function isArrayAllKeySequential($value)
     protected function addAttributes(DOMElement $element, array $data)
     {
         foreach ($data as $attrKey => $attrVal) {
-            $element->setAttribute($attrKey, $attrVal);
+            $element->setAttribute($attrKey, $attrVal ?? '');
         }
     }