500 error

image: 'gitlab/gitlab-ce:13.5.3-ce.0'

group settings：

`web_1  | ==> /var/log/gitlab/gitlab-rails/production_json.log <==
web_1  | {"method":"GET","path":"/groups/java/-/edit","format":"html","controller":"GroupsController","action":"edit","status":500,"time":"2020-11-09T09:45:25.210Z","params":[{"key":"id","value":"java"}],"remote_ip":"119.57.161.67","user_id":1,"username":"root","ua":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.183 Safari/537.36","correlation_id":"4Jk3UnkF7x7","meta.user":"root","meta.root_namespace":"java","meta.caller_id":"GroupsController#edit","meta.feature_category":"subgroups","redis_calls":9,"redis_duration_s":0.001555,"redis_read_bytes":1726,"redis_write_bytes":1279,"redis_cache_calls":8,"redis_cache_duration_s":0.001243,"redis_cache_read_bytes":1543,"redis_cache_write_bytes":405,"redis_shared_state_calls":1,"redis_shared_state_duration_s":0.000312,"redis_shared_state_read_bytes":183,"redis_shared_state_write_bytes":874,"queue_duration_s":0.003555,"cpu_s":0.05,"exception.class":"ActionView::Template::Error","exception.message":"undefined method `allow_mfa_for_subgroups' for nil:NilClass","exception.backtrace":["app/views/groups/settings/_two_factor_auth.html.haml:21","app/views/groups/settings/_permissions.html.haml:41","app/views/groups/settings/_permissions.html.haml:1","app/views/groups/edit.html.haml:27","app/controllers/application_controller.rb:134:in `render'","app/controllers/application_controller.rb:493:in `set_current_admin'","lib/gitlab/session.rb:11:in `with_session'","app/controllers/application_controller.rb:484:in `set_session_storage'","lib/gitlab/i18n.rb:73:in `with_locale'","lib/gitlab/i18n.rb:79:in `with_user_locale'","app/controllers/application_controller.rb:478:in `set_locale'","lib/gitlab/error_tracking.rb:52:in `with_context'","app/controllers/application_controller.rb:543:in `sentry_context'","app/controllers/application_controller.rb:471:in `block in set_current_context'","lib/gitlab/application_context.rb:54:in `block in use'","lib/gitlab/application_context.rb:54:in `use'","lib/gitlab/application_context.rb:21:in `with_context'","app/controllers/application_controller.rb:463:in `set_current_context'","lib/gitlab/metrics/elasticsearch_rack_middleware.rb:16:in `call'","lib/gitlab/middleware/rails_queue_duration.rb:33:in `call'","lib/gitlab/metrics/rack_middleware.rb:16:in `block in call'","lib/gitlab/metrics/transaction.rb:61:in `run'","lib/gitlab/metrics/rack_middleware.rb:16:in `call'","lib/gitlab/request_profiler/middleware.rb:17:in `call'","lib/gitlab/jira/middleware.rb:19:in `call'","lib/gitlab/middleware/go.rb:20:in `call'","lib/gitlab/etag_caching/middleware.rb:13:in `call'","lib/gitlab/middleware/multipart.rb:234:in `call'","lib/gitlab/middleware/handle_null_bytes.rb:19:in `call'","lib/gitlab/middleware/read_only/controller.rb:51:in `call'","lib/gitlab/middleware/read_only.rb:18:in `call'","lib/gitlab/middleware/same_site_cookies.rb:27:in `call'","lib/gitlab/middleware/basic_health_check.rb:25:in `call'","lib/gitlab/middleware/handle_ip_spoof_attack_error.rb:25:in `call'","lib/gitlab/middleware/request_context.rb:23:in `call'","config/initializers/fix_local_cache_middleware.rb:9:in `call'","lib/gitlab/metrics/requests_rack_middleware.rb:49:in `call'","lib/gitlab/middleware/release_env.rb:12:in `call'"],"db_duration_s":0.00865,"view_duration_s":0.0,"duration_s":0.04567,"db_count":12,"db_write_count":0,"db_cached_count":1}
web_1  | 
web_1  | ==> /var/log/gitlab/gitlab-rails/production.log <==
web_1  |   
web_1  | ActionView::Template::Error (undefined method `allow_mfa_for_subgroups' for nil:NilClass):
web_1  |     18: - unless group.has_parent?
web_1  |     19:   .form-group
web_1  |     20:     .form-check
web_1  |     21:       = f.check_box :allow_mfa_for_subgroups, class: 'form-check-input', checked: group.namespace_settings.allow_mfa_for_subgroups
web_1  |     22:       = f.label :allow_mfa_for_subgroups, class: 'form-check-label' do
web_1  |     23:         = _('Allow subgroups to set up their own two-factor authentication rules')
web_1  |   
web_1  | app/views/groups/settings/_two_factor_auth.html.haml:21
web_1  | app/views/groups/settings/_permissions.html.haml:41
web_1  | app/views/groups/settings/_permissions.html.haml:1
web_1  | app/views/groups/edit.html.haml:27
web_1  | app/controllers/application_controller.rb:134:in `render'
web_1  | app/controllers/application_controller.rb:493:in `set_current_admin'
web_1  | lib/gitlab/session.rb:11:in `with_session'
web_1  | app/controllers/application_controller.rb:484:in `set_session_storage'
web_1  | lib/gitlab/i18n.rb:73:in `with_locale'
web_1  | lib/gitlab/i18n.rb:79:in `with_user_locale'
web_1  | app/controllers/application_controller.rb:478:in `set_locale'
web_1  | lib/gitlab/error_tracking.rb:52:in `with_context'
web_1  | app/controllers/application_controller.rb:543:in `sentry_context'
web_1  | app/controllers/application_controller.rb:471:in `block in set_current_context'
web_1  | lib/gitlab/application_context.rb:54:in `block in use'
web_1  | lib/gitlab/application_context.rb:54:in `use'
web_1  | lib/gitlab/application_context.rb:21:in `with_context'
web_1  | app/controllers/application_controller.rb:463:in `set_current_context'
web_1  | lib/gitlab/metrics/elasticsearch_rack_middleware.rb:16:in `call'
web_1  | lib/gitlab/middleware/rails_queue_duration.rb:33:in `call'
web_1  | lib/gitlab/metrics/rack_middleware.rb:16:in `block in call'
web_1  | lib/gitlab/metrics/transaction.rb:61:in `run'
web_1  | lib/gitlab/metrics/rack_middleware.rb:16:in `call'
web_1  | lib/gitlab/request_profiler/middleware.rb:17:in `call'
web_1  | lib/gitlab/jira/middleware.rb:19:in `call'
web_1  | lib/gitlab/middleware/go.rb:20:in `call'
web_1  | lib/gitlab/etag_caching/middleware.rb:13:in `call'
web_1  | lib/gitlab/middleware/multipart.rb:234:in `call'
web_1  | lib/gitlab/middleware/handle_null_bytes.rb:19:in `call'
web_1  | lib/gitlab/middleware/read_only/controller.rb:51:in `call'
web_1  | lib/gitlab/middleware/read_only.rb:18:in `call'
web_1  | lib/gitlab/middleware/same_site_cookies.rb:27:in `call'
web_1  | lib/gitlab/middleware/basic_health_check.rb:25:in `call'
web_1  | lib/gitlab/middleware/handle_ip_spoof_attack_error.rb:25:in `call'
web_1  | lib/gitlab/middleware/request_context.rb:23:in `call'
web_1  | config/initializers/fix_local_cache_middleware.rb:9:in `call'
web_1  | lib/gitlab/metrics/requests_rack_middleware.rb:49:in `call'
web_1  | lib/gitlab/middleware/release_env.rb:12:in `call'
web_1  | `