fix(graphql): do not crash if attestation is nil

spec/graphql/dossier_spec.rb

@@ -0,0 +1,45 @@
+RSpec.describe Types::DossierType, type: :graphql do
+  let(:query) { DOSSIER_QUERY }
+  let(:context) { { internal_use: true } }
+  let(:variables) { {} }
+
+  subject { API::V2::Schema.execute(query, variables: variables, context: context) }
+
+  let(:data) { subject['data'].deep_symbolize_keys }
+  let(:errors) { subject['errors'].deep_symbolize_keys }
+
+  describe 'dossier with attestation' do
+    let(:dossier) { create(:dossier, :accepte, :with_attestation) }
+    let(:query) { DOSSIER_WITH_ATTESTATION_QUERY }
+    let(:variables) { { number: dossier.id } }
+
+    it { expect(data[:dossier][:attestation]).not_to be_nil }
+
+    context 'when attestation is nil' do
+      before do
+        dossier.update(attestation: nil)
+      end
+
+      it { expect(data[:dossier][:attestation]).to be_nil }
+    end
+  end
+
+  DOSSIER_QUERY = <<-GRAPHQL
+  query($number: Int!) {
+    dossier(number: $number) {
+      id
+      number
+    }
+  }
+  GRAPHQL
+
+  DOSSIER_WITH_ATTESTATION_QUERY = <<-GRAPHQL
+  query($number: Int!) {
+    dossier(number: $number) {
+      attestation {
+        url
+      }
+    }
+  }
+  GRAPHQL
+end