[FIX] Tax is mandatory on invoice lines

[BT-aestebanez]

Fix for #196

The standard does require at least one tax per invoice line as defined in the xsd:

  <xs:complexType name="LineTradeSettlementType">
    <xs:sequence>
      <xs:element name="ApplicableTradeTax" type="ram:TradeTaxType"/>
      <xs:element name="BillingSpecifiedPeriod" type="ram:SpecifiedPeriodType" minOccurs="0"/>
      <xs:element name="SpecifiedTradeAllowanceCharge" type="ram:TradeAllowanceChargeType" minOccurs="0" maxOccurs="unbounded"/>
      <xs:element name="SpecifiedTradeSettlementLineMonetarySummation" type="ram:TradeSettlementLineMonetarySummationType"/>
      <xs:element name="AdditionalReferencedDocument" type="ram:ReferencedDocumentType" minOccurs="0"/>
      <xs:element name="ReceivableSpecifiedTradeAccountingAccount" type="ram:TradeAccountingAccountType" minOccurs="0"/>
    </xs:sequence>
  </xs:complexType>

The element <xs:element name="ApplicableTradeTax" type="ram:TradeTaxType"/> does not have "minOccurs" set and therefore, the element is required (source https://www.w3schools.com/xml/schema_complex_indicators.asp)

[BT-aestebanez]

Hello @alexis-via
First of all thanks for contributing with this work.

Could you review this PR?

Thanks,
Alvaro

[thomaspaulb]

'specifies'.

[BT-aestebanez]

Thanks, applied

[alexis-via]

in my v14 PR to migrate account_invoice_facturx #288
I solved the problem when there is no tax on the invoice line, but I made big changes to the code that generate the tax block. Maybe we could backport it to v12. Could you have a look at it and tell me what you think ?

[alexis-via]

I forgot to mention that backporting is not easy due to the revolution on invoices in v13... tell me what you think first and then we'll decide.

[thomaspaulb]

Specifically this part, which adds an empty tax block if tax is not filled, right?

I'd say backporting that is an honourable but cumbersome job, and could be done later, on top of this small fix.

[BT-aestebanez]

Specifically this part, which adds an empty tax block if tax is not filled, right?

I'd say backporting that is an honourable but cumbersome job, and could be done later, on top of this small fix.

I agree :)
Sorry for the late reply

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