#php serialize() encodes null's as 'N' php serialize() encodes null's as the character 'N' http://php.net/manual/en/language.oop5.serialization.php http://php.net/manual/en/function.serialize.php#66147 IN <?php $a = array('a'=>123,'b'=>NULL); echo serialize($a); ?> OUT a:2:{s:1:"a";i:123;s:1:"b";N;} encode null php serialise serialize