[IMP] util.update_record_from_xml

Sometimes records get a field removed from their XML declaration. This creates a
divergence between new dbs and upgraded ones. The former will be initialised
with `NULL`/default values, whereas the latter will retain their current one.
This is usually handled in dedicated upgrade scripts with simple queries
unsetting the necessary columns. However, in some cases, these XML changes are
backported/noticed too late and need to be addressed in multiple versions.
That may create the pressure to target future versions, which creates a hidden
coupling between the xml declaration and the query, which can easily turn into a
bug. It is one such example[^1] that inspired this PR.

The proposed solution is to adapt `update_record_from_xml` to unset fields from
the `fields` kwarg and missing from the XML declaration ensuring foreward
compatibility.

[^1]: odoo/upgrade#9512

Author: Pirols

src/util/records.py

@@ -1039,7 +1039,8 @@ def update_record_from_xml(
                                    should also be updated.
     :param set(str) or None fields: optional list of fields to include in the XML declaration.
                                     If set, all other fields will be ignored. When set, record
-                                    won't be created if missing.
+                                    won't be created if missing and all fields not found in
+                                    the XML declaration will be set to NULL.
 
     .. warning::
        This functions uses the ORM, therefore it can only be used after **all** models
@@ -1147,9 +1148,13 @@ def add_ref(ref):
                 found = True
                 parent = node.getparent()
                 if node.tag == "record" and fields is not None:
+                    fields_to_find = set(fields)
                     for fn in node.xpath("./field[@name]"):
                         if fn.attrib["name"] not in fields:
                             node.remove(fn)
+                        else:
+                            fields_to_find.remove(fn.attrib["name"])
+                    node.extend(lxml.builder.E.field(name=field_name, eval="False") for field_name in fields_to_find)
                 new_root[0].append(node)
 
                 if node.tag == "menuitem" and parent.tag == "menuitem" and "parent_id" not in node.attrib: