diff --git a/fields/field.memberactivation.php b/fields/field.memberactivation.php
index 15c1d2c..bb5e66a 100644
--- a/fields/field.memberactivation.php
+++ b/fields/field.memberactivation.php
@@ -208,7 +208,7 @@ public function displaySettingsPanel(XMLElement &$wrapper, $errors = NULL){
 				"fields[{$this->get('sortorder')}][code_expiry]", $this->get('code_expiry')
 			));
 
-			$ul = new XMLElement('ul', NULL, array('class' => 'tags singular', 'data-interactive' => 'data-interactive'));
+			$ul = new XMLElement('ul', null, array('class' => 'tags singular', 'data-interactive' => 'data-interactive'));
 			$tags = fieldMemberActivation::findCodeExpiry();
 			foreach($tags as $name => $time) {
 				$ul->appendChild(new XMLElement('li', $name, array('class' => $time)));