diff --git a/core/class/helper.class.php b/core/class/helper.class.php
index e4c9aa59..70a646c9 100644
--- a/core/class/helper.class.php
+++ b/core/class/helper.class.php
@@ -333,7 +333,7 @@ class helper {
 	 * @return string
 	 */
 	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;