diff --git a/src/Attribute.php b/src/Attribute.php
index 84f13c0..e8d2415 100644
--- a/src/Attribute.php
+++ b/src/Attribute.php
@@ -108,7 +108,7 @@ public function toXML(DOMElement $parent): DOMElement
     {
         $parent->setAttributeNS(
             $this->getNamespaceURI(),
-            ($this->getNamespacePrefix() !== '')
+            in_array($this->getNamespacePrefix(), ['', null])
                 ? ($this->getNamespacePrefix() . ':' . $this->getAttrName())
                 : $this->getAttrName(),
             $this->getAttrValue(),