[FIX] base_address_extended: default to Null instead of empty string

for computed street fields.

Qweb reports delete the node if the value is Null but won't if the value is an empty string. And then, l10n_mx_edi module has errors because there are nodes with empty string and the minimum value is one char.

Courtesy of Vauxoo. Was PR #17169

Backport in Saas-14 from opw-770430

addons/base_address_extended/models/base_address_extended.py

@@ -91,7 +91,7 @@ class Partner(models.Model):
         for partner in self:
             if not partner.street:
                 for field in street_fields:
-                    partner[field] = ''
+                    partner[field] = None
                 continue
 
             street_format = (partner.country_id.street_format or