[19.0][OU-FIX] account_edi_ubl_cii: guard map_values when source column is absent

[mvalee]

Problem

The account_edi_ubl_cii 19.0 pre-migration script calls openupgrade.map_values()
on account_tax.ubl_cii_tax_exemption_reason_code, but that column is not present
on every 18.0 database (e.g. Community installs that never stored it). On such a DB
the migration aborts:

psycopg2.errors.UndefinedColumn: column "ubl_cii_tax_exemption_reason_code" does not exist
ERROR ... OpenUpgrade: account_edi_ubl_cii: error in migration script
         .../account_edi_ubl_cii/19.0.1.0/pre-migration.py
CRITICAL ... Failed to initialize database `<db>`.

Because it runs during -u all, the whole 18.0 -> 19.0 upgrade fails, not just this module.

Hit while migrating a real Belgian Community 18.0 -> 19.0 database.

Fix

Guard the value remap with openupgrade.column_exists(). When the column is absent
there is nothing to remap, and the 19.0 module update creates it afterwards, so
skipping is correct (not a workaround).

Verification

With the guard, a full -u all 18.0 -> 19.0 upgrade completes on a Community database
that lacks the column (176 modules loaded), with data and accounting balances intact.

[hbrunn]

how can this happen? that's more interesting than the generated bullshit below

[aurelien-tempo]

Hello,
I just had the case during my migration from 16 to 19.
In 18, the account_edi_ubl_cii module is auto-installed if you have the account module, while the account_edi_ubl_cii_tax_extension isn't.
In 19, the 2nd module was merged into the 1st one.
So if you had account_edi_ubl_cii but not account_edi_ubl_cii_tax_extension in 18, the column does not exist yet.

[hbrunn]

so please write a condensed version of this in the comment, and delete the rest

[aurelien-tempo]

@mvalee could you please update the comment so that it can be merged ?

[mvalee]

have adapted