diff --git a/core/class/helper.class.php b/core/class/helper.class.php
index 0bc41a9e..ca32b975 100644
--- a/core/class/helper.class.php
+++ b/core/class/helper.class.php
@@ -393,7 +393,7 @@ class helper
 	 */
 	public static function filter($text, $filter)
 	{
-		$text = trim($text);
+		$text = is_null($text) ? $text : trim($text);
 		switch ($filter) {
 			case self::FILTER_BOOLEAN:
 				$text = (bool) $text;