Add missing spec

spec/graphql/resolvers/design_management/designs_resolver_spec.rb

@@ -65,6 +65,22 @@ RSpec.describe Resolvers::DesignManagement::DesignsResolver do
         let(:second_version) { create(:design_version) }
         let(:second_design) { create(:design, issue: issue, versions: [second_version]) }
 
+        context 'ids is provided but null' do
+          let(:args) { { ids: nil } }
+
+          it 'behaves as if unfiltered' do
+            expect(resolve_designs).to contain_exactly(first_design, second_design)
+          end
+        end
+
+        context 'ids is provided but empty' do
+          let(:args) { { ids: [] } }
+
+          it 'eliminates all values' do
+            expect(resolve_designs).to be_empty
+          end
+        end
+
         context 'the ID is on the current issue' do
           let(:args) { { ids: [GitlabSchema.id_from_object(second_design)] } }