eZ\Publish\Core\FieldType\Date\Type::toHash PHP Method

    public function toHash(SPIValue $value)
    {
        if ($this->isEmptyValue($value)) {
            return null;
        }
        if ($value->date instanceof DateTime) {
            return array('timestamp' => $value->date->getTimestamp(), 'rfc850' => $value->date->format(DateTime::RFC850));
        }
        return array('timestamp' => 0, 'rfc850' => null);
    }