Return an empty array when no matches are found

app/models/concerns/group_descendant.rb

@@ -6,7 +6,7 @@ module GroupDescendant
 
   def self.build_hierarchy(descendants, hierarchy_top = nil)
     descendants = Array.wrap(descendants)
-    return if descendants.empty?
+    return [] if descendants.empty?
 
     unless descendants.all? { |hierarchy| hierarchy.is_a?(GroupDescendant) }
       raise ArgumentError.new('element is not a hierarchy')

spec/controllers/groups_controller_spec.rb

@@ -331,6 +331,16 @@ describe GroupsController do
           expect(response).to have_http_status(200)
         end
 
+        it 'returns an empty array when there are no search results' do
+          subgroup = create(:group, :public, parent: group)
+          l2_subgroup = create(:group, :public, parent: subgroup)
+          create(:project, :public, namespace: l2_subgroup, name: 'no-match')
+
+          get :children, id: subgroup.to_param, filter: 'test', format: :json
+
+          expect(json_response).to eq([])
+        end
+
         it 'includes pagination headers' do
           2.times { |i| create(:group, :public, parent: public_subgroup, name: "filterme#{i}") }