diff --git a/preferences/inc/class.preferences_settings.inc.php b/preferences/inc/class.preferences_settings.inc.php
index 9c2f95be7a..57f0623311 100644
--- a/preferences/inc/class.preferences_settings.inc.php
+++ b/preferences/inc/class.preferences_settings.inc.php
@@ -411,7 +411,7 @@ class preferences_settings
 		return null;
 	}
 
-	public static function defaultLabel(string $type='user')
+	public static function defaultLabel(?string $type='user')
 	{
 		switch($type)
 		{