Start your trial page returns 500 error

https://gitlab.cn/-/trials/new?glm_content=gold-callout&glm_source=gitlab.com

Error logs

*** /var/log/gitlab/production.log ***
Sending event 8fe2e1627f6749d69087372dd5666b9e to Sentry

ActionView::Template::Error (undefined method `use_backwards_compatible_subject_index' for nil:NilClass):
    12:     = render 'errors'
    13:
    14:     = form_tag create_lead_trials_path(glm_params), method: :post do |f|
    15:       - if experiment_enabled?(:remove_known_trial_form_fields) && current_user.first_name.present?
    16:         = hidden_field_tag :first_name, current_user.first_name
    17:       - else
    18:         .form-group

lib/gitlab/experimentation/controller_concern.rb:112:in `fallback_experimentation_subject_index'
lib/gitlab/experimentation/controller_concern.rb:51:in `experiment_enabled?'
lib/gitlab/experimentation/controller_concern.rb:20:in `experiment_enabled?'
app/controllers/application_controller.rb:124:in `render'
ee/lib/gitlab/ip_address_state.rb:10:in `with'
ee/app/controllers/ee/application_controller.rb:44:in `set_current_ip_address'
app/controllers/application_controller.rb:483:in `set_current_admin'
lib/gitlab/session.rb:11:in `with_session'
app/controllers/application_controller.rb:474:in `set_session_storage'
lib/gitlab/i18n.rb:99:in `with_locale'
lib/gitlab/i18n.rb:105:in `with_user_locale'
app/controllers/application_controller.rb:468:in `set_locale'
app/controllers/application_controller.rb:462:in `set_current_context'
ee/lib/omni_auth/strategies/group_saml.rb:41:in `other_phase'
lib/gitlab/metrics/elasticsearch_rack_middleware.rb:16:in `call'
lib/gitlab/middleware/rails_queue_duration.rb:33:in `call'
lib/gitlab/middleware/speedscope.rb:13:in `call'
lib/gitlab/request_profiler/middleware.rb:17:in `call'
lib/gitlab/database/load_balancing/rack_middleware.rb:40:in `call'
lib/gitlab/metrics/rack_middleware.rb:16:in `block in call'
lib/gitlab/metrics/web_transaction.rb:21:in `run'
lib/gitlab/metrics/rack_middleware.rb:16:in `call'
lib/gitlab/jira/middleware.rb:19:in `call'
lib/gitlab/middleware/go.rb:20:in `call'
lib/gitlab/etag_caching/middleware.rb:21:in `call'
lib/gitlab/middleware/multipart.rb:172:in `call'
lib/gitlab/middleware/read_only/controller.rb:50:in `call'
lib/gitlab/middleware/read_only.rb:18:in `call'
lib/gitlab/middleware/same_site_cookies.rb:27:in `call'
lib/gitlab/middleware/handle_malformed_strings.rb:21: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:21:in `call'
config/initializers/fix_local_cache_middleware.rb:11:in `call'
lib/gitlab/middleware/rack_multipart_tempfile_factory.rb:19:in `call'
lib/gitlab/metrics/requests_rack_middleware.rb:74:in `call'
lib/gitlab/middleware/release_env.rb:12:in `call'