protected function is0VatRate($vatRate)
    {
        if (is_array($vatRate) && isset($vatRate)) {
            $vatRate = isset($vatRate[Tag::VatRate]) ? $vatRate[Tag::VatRate] : null;
        }
        return isset($vatRate) && (Number::isZero($vatRate) || Number::floatsAreEqual($vatRate, -1.0));
    }