fix(address): BAN does not return postcode for some TOM like Nouvelle-Calédonie

But we have to fallback to an empty string because API graphql / serializer
expects a non-null attribute.

app/models/champs/address_champ.rb

@@ -97,9 +97,13 @@ class Champs::AddressChamp < Champs::TextChamp
   end
 
   def commune_name
-    if full_address?
-      "#{APIGeoService.commune_name(code_departement, address['city_code'])} (#{address['postal_code']})"
-    end
+    return if !full_address?
+
+    commune = APIGeoService.commune_name(code_departement, address['city_code'])
+
+    return commune if address['postal_code'].blank?
+
+    "#{commune} (#{address['postal_code']})"
   end
 
   def commune

app/services/api_geo_service.rb

@@ -115,7 +115,7 @@ class APIGeoService
         label: properties.fetch('label'),
         type: properties.fetch('type'),
         street_address: properties.fetch('name'),
-        postal_code: properties.fetch('postcode'),
+        postal_code: properties.fetch('postcode') { '' }, # API graphql / serializer requires non-null data
         street_number: properties['housenumber'],
         street_name: properties['street'],
         geometry: feature['geometry']