This update adjusts the handling of tax exemption reasons in UBL (Universal Business Language) documents. Now, users can omit the specific tax exemption reason code when it's not required by the ubl standard. A default reason is automatically applied for appropriate tax categories, ensuring compliance and simplifying the process.

According to the ubl documentation the tax exemption reason code is not
always required on the document. But when no exemption reason code is 
given, we have a default exemption reason for the appropriate tax 
categories.


task: 5223145

Forward-Port-Of: odoo/odoo#233770