public function guard($value, Field $field)
    {
        Assertion::integer($value, null, $field->getName());
        Assertion::true(
            DateUtils::isValidTimestamp($value),
            sprintf('Field [%s] value [%d] is not a valid unix timestamp.', $field->getName(), $value),
            $field->getName()
        );
    }
public function guard($value, Field $field)
    {
        Assertion::integer($value, null, $field->getName());
        Assertion::true(
            DateUtils::isValidTimestamp($value),
            sprintf('Field [%s] value [%d] is not a valid unix timestamp.', $field->getName(), $value),
            $field->getName()
        );
    }
{@inheritdoc}