diff --git a/include/functions.php b/include/functions.php
index 14de32e95..f4a218ce3 100644
--- a/include/functions.php
+++ b/include/functions.php
@@ -267,7 +267,7 @@
 	 *
 	 * @param mixed $param
 	 *
-	 * @return mixed
+	 * @return mixed|null
 	 */
 	function clean($param) {
 		if (is_array($param)) {