protected function removeValuesNotToBeStored(array $values)
    {
        $result = array();
        $keys = $this->getKeys();
        $defaults = $this->getDefaults();
        foreach ($keys as $key) {
            if (isset($values[$key]) && (!isset($defaults[$key]) || $values[$key] !== $defaults[$key])) {
                $result[$key] = $values[$key];
            }
        }
        return $result;
    }