more robust normalization

app/services/api_geo_service.rb

@@ -101,7 +101,7 @@ class APIGeoService
           department_code:,
           region_name: region_name(region_code),
           region_code:,
-          city_name: commune_name(department_code, city_code) || properties['city'], # fallback to city name if commune not found
+          city_name: safely_normalize_city_name(department_code, city_code, properties['city']),
           city_code:
         }
       else
@@ -122,6 +122,15 @@ class APIGeoService
       }.merge(territory)
     end
 
+    def safely_normalize_city_name(department_code, city_code, fallback)
+      return fallback if department_code.nil? || city_code.nil?
+
+      commune_name(department_code, city_code) || fallback
+
+    rescue StandardError
+      fallback
+    end
+
     private
 
     def communes_by_postal_code_map

spec/services/api_geo_service_spec.rb

@@ -107,4 +107,34 @@ describe APIGeoService do
       it { expect(subject[:city_name]).to eq('Paris') }
     end
   end
+
+  describe 'safely_normalize_city_name' do
+    let(:department_code) { '75' }
+    let(:city_code) { '75056' }
+    let(:fallback) { 'Paris' }
+
+    subject { APIGeoService.safely_normalize_city_name(department_code, city_code, fallback) }
+
+    context 'nominal' do
+      it { is_expected.to eq('Paris') }
+    end
+
+    context 'without department' do
+      let(:department_code) { nil }
+
+      it { is_expected.to eq('Paris') }
+    end
+
+    context 'without city_code' do
+      let(:city_code) { nil }
+
+      it { is_expected.to eq('Paris') }
+    end
+
+    context 'with a wrong department' do
+      let(:department_code) { 'wrong' }
+
+      it { is_expected.to eq('Paris') }
+    end
+  end
 end