[FIX] account_edi_ubl_cii: ensure key existence

**Current behavior:**
Creating a fixed tax with the edi formats ubl_bis3 and nlcius_1
then creating an invoice with this tax tied to a product will
cause a traceback when a user tries to confirm the invoice.

**Expected behavior:**
The invoice will post as any other might.

**Steps to reproduce:**
1. Create a NL company with l10n_nl_edi accounting

2. Create a tax with the following field values:
     *tax computation: fixed*
     *affect base of subsequent taxes: True*
     *base affected by previous taxes: True*

3. In the customer invoices journal for the created company,
     go to the 'Advanced Settings' notebook tab and enable the
     NLCIUS and Peppol options under 'Electronic Invoicing'

4. Create a new invoice with some product and attach the newly
     created tax to it, then try to confirm the invoice to see
     the traceback

**Cause of the issue:**
The edi format tags invoke different instances of the
get_invoice_line_allowance_vals_list() method. This method
returns a dict list where the dicts only sometimes contain the
key 'allowance_charge_reason_code'. A subsequent expression
expects this key in the dict which can cause a KeyError.

**Fix:**
Check instead for a 'charge_indicator' key, which is present in
both the ubl_bis3 and nlcius_1 val dicts, allowing the correct
total to be summed and reflected in the EDI document output.

opw-3680527

closes odoo/odoo#157495

X-original-commit: 06a3027ca9f421ccc0081e2c8a5ff538175ef334
Signed-off-by: Laurent Smet (las) <las@odoo.com>
Signed-off-by: Vincent Ethan <etvi@odoo.com>

addons/account_edi_ubl_cii/models/account_edi_xml_ubl_20.py

@@ -362,7 +362,7 @@ class AccountEdiXmlUBL20(models.AbstractModel):
         total_fixed_tax_amount = sum(
             vals['amount']
             for vals in allowance_charge_vals_list
-            if vals['allowance_charge_reason_code'] == 'AEO'
+            if vals.get('charge_indicator') == 'true'
         )
         return {
             'currency': line.currency_id,

addons/l10n_account_edi_ubl_cii_tests/tests/test_xml_ubl_nl.py

@@ -1,6 +1,9 @@
 # -*- coding: utf-8 -*-
 from odoo.addons.l10n_account_edi_ubl_cii_tests.tests.common import TestUBLCommon
 from odoo.tests import tagged
+from odoo import Command
+
+from lxml import etree
 
 
 @tagged('post_install_l10n', 'post_install', '-at_install')
@@ -68,6 +71,16 @@ class TestUBLNL(TestUBLCommon):
             'amount': 7,
             'type_tax_use': 'purchase',
             'country_id': cls.env.ref('base.nl').id,
+            'sequence': 2,
+        })
+
+        cls.tax_10_fixed = cls.env['account.tax'].create({
+            'name': 'Test Tax',
+            'amount_type': 'fixed',
+            'include_base_amount': True,
+            'country_id': cls.env.ref('base.nl').id,
+            'amount': 10.0,
+            'sequence': 1,
         })
 
     @classmethod
@@ -201,6 +214,24 @@ class TestUBLNL(TestUBLCommon):
         self.assertEqual(attachment.name[-10:], "nlcius.xml")
         self._assert_imported_invoice_from_etree(refund, attachment)
 
+    def test_export_fixed_tax(self):
+        """
+        Ensure that an invoice containing a product with a fixed tax posted to a journal with the peppol and nlcius edi
+            tags generates edi documents with accurate LineExtensionAmount values
+        """
+        invoice = self._generate_move(
+            self.partner_1, self.partner_2,
+            move_type='out_invoice',
+            invoice_line_ids=[{
+                'name': 'product costing 50.0',
+                'quantity': 1,
+                'price_unit': 50.0,
+                'tax_ids': [Command.set([self.tax_10_fixed.id, self.tax_7_purchase.id])]
+            }]
+        )
+        amount = etree.fromstring(invoice.ubl_cii_xml_id.raw).find('.//{*}LegalMonetaryTotal/{*}LineExtensionAmount').text
+        self.assertEqual(amount, '60.00')
+
     ####################################################
     # Test import
     ####################################################