public function getDifference()
{
if ($this->_old === null) {
return $this->_new !== null ? $this->_new->toArray() : $this->_null;
} else {
$new = $this->_new->toArray();
$old = $this->_old->toArray();
$diff = array_diff_assoc($new, $old);
return count($diff) > 0 ? $diff : $this->_null;
}
}