fix(graphql): return empty arrays from loaders when loading collections

app/graphql/loaders/champ.rb

@@ -13,7 +13,7 @@ module Loaders
 
     def perform(keys)
       query(keys).each { |record| fulfill(record.stable_id, [record].compact) }
-      keys.each { |key| fulfill(key, nil) unless fulfilled?(key) }
+      keys.each { |key| fulfill(key, []) unless fulfilled?(key) }
     end
 
     private

app/graphql/loaders/record.rb

@@ -21,7 +21,7 @@ module Loaders
         fulfilled_value = @array ? [record].compact : record
         fulfill(record.public_send(@column), fulfilled_value)
       end
-      keys.each { |key| fulfill(key, nil) unless fulfilled?(key) }
+      keys.each { |key| fulfill(key, @array ? [] : nil) unless fulfilled?(key) }
     end
 
     private

spec/graphql/dossier_spec.rb

@@ -75,6 +75,27 @@ RSpec.describe Types::DossierType, type: :graphql do
     end
   end
 
+  describe 'dossier with selected champ' do
+    let(:procedure) { create(:procedure, types_de_champ_public: [{ libelle: 'yolo' }, { libelle: 'toto' }]) }
+    let(:dossier) { create(:dossier, :en_construction, :with_populated_champs, procedure:) }
+    let(:query) { DOSSIER_WITH_SELECTED_CHAMP_QUERY }
+    let(:variables) { { number: dossier.id, id: champ.to_typed_id } }
+    let(:champ) { dossier.champs_public.last }
+
+    context 'when champ exists' do
+      it {
+        expect(data[:dossier][:champs].size).to eq 1
+        expect(data[:dossier][:champs][0][:label]).to eq "toto"
+      }
+    end
+
+    context "when champ dosen't exists" do
+      let(:variables) { { number: dossier.id, id: '1234' } }
+
+      it { expect(data[:dossier][:champs].size).to eq 0 }
+    end
+  end
+
   describe 'dossier with conditional champs' do
     include Logic
     let(:stable_id) { 1234 }
@@ -390,4 +411,15 @@ RSpec.describe Types::DossierType, type: :graphql do
     }
   }
   GRAPHQL
+
+  DOSSIER_WITH_SELECTED_CHAMP_QUERY = <<-GRAPHQL
+  query($number: Int!, $id: ID!) {
+    dossier(number: $number) {
+      champs(id: $id) {
+        id
+        label
+      }
+    }
+  }
+  GRAPHQL
 end