protected function correct0VatToVatFree()
    {
        if (isset($this->invoice[Tag::Customer][Tag::Invoice][Tag::VatType])) {
            $vatType = $this->invoice[Tag::Customer][Tag::Invoice][Tag::VatType];
            if (in_array($vatType, static::$vatTypesAllowingVatFree)) {
                foreach ($this->invoice[Tag::Customer][Tag::Invoice][Tag::Line] as &$line) {
                    if ($this->lineHas0VatRate($line)) {
                        $line[Tag::VatRate] = Api::VatFree;
                    }
                }
            }
        }
    }