[FIX+MIG] base_location: 3 things:

* Don't need cities for migrating

  Previous script required to have cities populated for working, but that's not
  usual thing, as people in v11 may choose to not import them, and for older databases
  they even weren't that option.

  With this improve script, now we populate city table for ZIP entries without city,
  so the rest of the queries are properly executed in any case.

* Cover case of res_better_zip w/o country_id

* Avoid error on null zip numbers

base_location/migrations/12.0.1.0.0/post-migration.py

@@ -12,6 +12,35 @@ def migrate(env, version):
         env.cr,
         "ALTER TABLE res_city_zip ADD %s INTEGER", (AsIs(column_name), ),
     )
+    # Create a city for ZIPs without it
+    openupgrade.logged_query(
+        env.cr, """
+        INSERT INTO res_city (
+            name, state_id, country_id,
+            create_uid, create_date, write_uid, write_date
+        )
+        SELECT
+            city, state_id, country_id,
+            MIN(create_uid), MIN(create_date), MIN(write_uid), MIN(write_date)
+        FROM res_better_zip rbz
+        WHERE city_id IS NULL
+            AND rbz.country_id IS NOT NULL
+            AND rbz.name IS NOT NULL
+        GROUP BY city, state_id, country_id
+        ON CONFLICT DO NOTHING""",
+    )
+    # Update city_id in res_better_zip
+    openupgrade.logged_query(
+        env.cr, """
+        UPDATE res_better_zip rbz
+        SET city_id = rc.id
+        FROM res_city rc
+        WHERE rc.name = rbz.city
+            AND rc.state_id = rbz.state_id
+            AND rc.country_id = rbz.country_id
+            AND rbz.city_id IS NULL""",
+    )
+    # Create records for new model
     openupgrade.logged_query(
         env.cr, """
         INSERT INTO res_city_zip (
@@ -20,7 +49,8 @@ def migrate(env, version):
         SELECT
             id, name, city_id
         FROM res_better_zip
-        WHERE city_id IS NOT NULL""",
+        WHERE city_id IS NOT NULL
+        ON CONFLICT DO NOTHING""",
         (AsIs(column_name), ),
     )
     # Recompute display name for entries inserted by SQL