Fix group membership CSV export for invited users

Previously, group members that didn't have an associated
user object would cause the CSV export to fail.

Fixes this to return nil if any of the row information
is unknown rather than throwing an error.

Also leaves the rescue statement in place to avoid
any repeated sidekiq failure and to record any further
failures.

Changelog: fixed

ee/app/services/groups/memberships/export_service.rb

@@ -21,8 +21,8 @@ module Groups
 
       def header_to_value_hash
         {
-          'Username' => 'user_username',
-          'Name'     => 'user_name',
+          'Username' => -> (member) { member&.user&.username },
+          'Name'     => -> (member) { member&.user&.name },
           'Access granted' => -> (member) { member.created_at.to_s(:csv) },
           'Access expires' => -> (member) { member.expires_at },
           'Max role' => 'human_access',

ee/app/workers/groups/export_memberships_worker.rb

@@ -16,10 +16,6 @@ module Groups
       @response = Groups::Memberships::ExportService.new(container: @group, current_user: @current_user).execute
 
       send_email if @response.success?
-    rescue Module::DelegationError => exception
-      # TEMPORARY: Rescue when a User record is not available,
-      # see https://gitlab.com/gitlab-org/gitlab/-/issues/338707
-      Raven.capture_exception(exception, tags: { group_id: @group.id, user_id: @current_user.id })
     end
 
     private

ee/spec/services/groups/memberships/export_service_spec.rb

@@ -89,6 +89,10 @@ RSpec.describe Groups::Memberships::ExportService do
         before do
           create_list(:group_member, 4, group: group)
           create(:group_member, group: group, created_at: '2021-02-01', expires_at: '2022-01-01', user: create(:user, username: 'mwoolf', name: 'Max Woolf'))
+          create(:group_member, :invited, group: group)
+          create(:group_member, :ldap, group: group)
+          create(:group_member, :blocked, group: group)
+          create(:group_member, :minimal_access, group: group)
         end
         let(:csv) { CSV.parse(service.execute.payload, headers: true) }
 
@@ -97,7 +101,7 @@ RSpec.describe Groups::Memberships::ExportService do
         end
 
         it 'has the correct number of rows' do
-          expect(csv.size).to eq(6)
+          expect(csv.size).to eq(9)
         end
 
         context 'a direct user', :aggregate_failures do

ee/spec/workers/groups/export_memberships_worker_spec.rb

@@ -19,18 +19,4 @@ RSpec.describe Groups::ExportMembershipsWorker do
 
     worker.perform(group.id, user.id)
   end
-
-  context 'when there is a Module::DelegationError' do
-    before do
-      allow_next_instance_of(Groups::Memberships::ExportService) do |service|
-        allow(service).to receive(:execute).and_raise(Module::DelegationError)
-      end
-    end
-
-    it 'rescues the exception' do
-      expect(Notify).not_to receive(:memberships_export_email)
-      expect(Raven).to receive(:capture_exception).and_call_original
-      worker.perform(group.id, user.id)
-    end
-  end
 end