500 Error when loading a specific topic

A user recently reported that a thread on my site started returning an Internal Server Error last night.

The thread is in Q&A format, but besides that it’s normal.

I dont know what’s causing this.

There’s another Q&A topic here which works fine.

Check the /logs page for the backtrace of the error 500.

I see this.

 35
Deprecation notice: `SiteSetting.secure_media` has been deprecated. Please use `SiteSetting.secure_uploads` instead. (removal in Discourse 3.0) At /var/www/discourse/lib/site_setting_extension.rb:211
11
NoMethodError (undefined method `name' for nil:NilClass) (eval):5:in `_fast_attributes' (eval):90:in `_fast_attributes' app/serializers/post_stream_serializer_mixin.rb:53:in `block in posts' app/seria
2:16 pm

plugins/discourse-question-answer/app/serializers/question_answer_comment_serializer.rb:17:in `name'
(eval):5:in `_fast_attributes'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:468:in `rescue in attributes'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:455:in `attributes'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:480:in `_serializable_hash'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:359:in `serializable_hash'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:347:in `as_json'
plugins/discourse-question-answer/extensions/post_serializer_extension.rb:27:in `block in comments'
plugins/discourse-question-answer/extensions/post_serializer_extension.rb:24:in `map'
plugins/discourse-question-answer/extensions/post_serializer_extension.rb:24:in `comments'
(eval):90:in `_fast_attributes'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:468:in `rescue in attributes'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:455:in `attributes'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:480:in `_serializable_hash'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:359:in `serializable_hash'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:347:in `as_json'
app/serializers/post_stream_serializer_mixin.rb:53:in `block in posts'
activerecord (7.0.3.1) lib/active_record/relation/delegation.rb:88:in `each'
activerecord (7.0.3.1) lib/active_record/relation/delegation.rb:88:in `each'
app/serializers/post_stream_serializer_mixin.rb:46:in `map'
app/serializers/post_stream_serializer_mixin.rb:46:in `posts'
plugins/discourse-reactions/lib/discourse_reactions/topic_view_serializer_extension.rb:17:in `posts'
app/serializers/post_stream_serializer_mixin.rb:18:in `post_stream'
(eval):3:in `_fast_attributes'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:468:in `rescue in attributes'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:455:in `attributes'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:480:in `_serializable_hash'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:359:in `serializable_hash'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:347:in `as_json'
activesupport (7.0.3.1) lib/active_support/json/encoding.rb:22:in `encode'
activesupport (7.0.3.1) lib/active_support/json/encoding.rb:22:in `encode'
activesupport (7.0.3.1) lib/active_support/core_ext/object/json.rb:42:in `to_json'
active_model_serializers (0.8.4) lib/active_model/serializer.rb:331:in `to_json'
multi_json (1.15.0) lib/multi_json/adapters/oj.rb:56:in `dump'
multi_json (1.15.0) lib/multi_json/adapters/oj.rb:56:in `dump'
multi_json (1.15.0) lib/multi_json/adapter.rb:25:in `dump'
multi_json (1.15.0) lib/multi_json.rb:139:in `dump'
app/controllers/topics_controller.rb:1199:in `block (2 levels) in perform_show_response'
actionpack (7.0.3.1) lib/action_controller/metal/mime_responds.rb:214:in `respond_to'
app/controllers/topics_controller.rb:1194:in `perform_show_response'
app/controllers/topics_controller.rb:169:in `show'
actionpack (7.0.3.1) lib/action_controller/metal/basic_implicit_render.rb:6:in `send_action'
actionpack (7.0.3.1) lib/abstract_controller/base.rb:215:in `process_action'
actionpack (7.0.3.1) lib/action_controller/metal/rendering.rb:53:in `process_action'
actionpack (7.0.3.1) lib/abstract_controller/callbacks.rb:234:in `block in process_action'
activesupport (7.0.3.1) lib/active_support/callbacks.rb:118:in `block in run_callbacks'
app/controllers/application_controller.rb:413:in `block in with_resolved_locale'
i18n (1.12.0) lib/i18n.rb:322:in `with_locale'
app/controllers/application_controller.rb:413:in `with_resolved_locale'
activesupport (7.0.3.1) lib/active_support/callbacks.rb:127:in `block in run_callbacks'
activesupport (7.0.3.1) lib/active_support/callbacks.rb:138:in `run_callbacks'
actionpack (7.0.3.1) lib/abstract_controller/callbacks.rb:233:in `process_action'
actionpack (7.0.3.1) lib/action_controller/metal/rescue.rb:22:in `process_action'
actionpack (7.0.3.1) lib/action_controller/metal/instrumentation.rb:67:in `block in process_action'
activesupport (7.0.3.1) lib/active_support/notifications.rb:206:in `block in instrument'
activesupport (7.0.3.1) lib/active_support/notifications/instrumenter.rb:24:in `instrument'
activesupport (7.0.3.1) lib/active_support/notifications.rb:206:in `instrument'
actionpack (7.0.3.1) lib/action_controller/metal/instrumentation.rb:66:in `process_action'
actionpack (7.0.3.1) lib/action_controller/metal/params_wrapper.rb:259:in `process_action'
activerecord (7.0.3.1) lib/active_record/railties/controller_runtime.rb:27:in `process_action'
actionpack (7.0.3.1) lib/abstract_controller/base.rb:151:in `process'
actionview (7.0.3.1) lib/action_view/rendering.rb:39:in `process'
rack-mini-profiler (3.0.0) lib/mini_profiler/profiling_methods.rb:85:in `block in profile_method'


actionpack (7.0.3.1) lib/action_controller/metal.rb:188:in `dispatch'
actionpack (7.0.3.1) lib/action_controller/metal.rb:251:in `dispatch'
actionpack (7.0.3.1) lib/action_dispatch/routing/route_set.rb:49:in `dispatch'
actionpack (7.0.3.1) lib/action_dispatch/routing/route_set.rb:32:in `serve'
actionpack (7.0.3.1) lib/action_dispatch/journey/router.rb:50:in `block in serve'
actionpack (7.0.3.1) lib/action_dispatch/journey/router.rb:32:in `each'
actionpack (7.0.3.1) lib/action_dispatch/journey/router.rb:32:in `serve'
actionpack (7.0.3.1) lib/action_dispatch/routing/route_set.rb:852:in `call'
lib/middleware/omniauth_bypass_middleware.rb:71:in `call'
rack (2.2.4) lib/rack/tempfile_reaper.rb:15:in `call'
rack (2.2.4) lib/rack/conditional_get.rb:27:in `call'
rack (2.2.4) lib/rack/head.rb:12:in `call'
actionpack (7.0.3.1) lib/action_dispatch/http/permissions_policy.rb:38:in `call'
lib/content_security_policy/middleware.rb:12:in `call'
lib/middleware/anonymous_cache.rb:368:in `call'
rack (2.2.4) lib/rack/session/abstract/id.rb:266:in `context'
rack (2.2.4) lib/rack/session/abstract/id.rb:260:in `call'
actionpack (7.0.3.1) lib/action_dispatch/middleware/cookies.rb:697:in `call'
actionpack (7.0.3.1) lib/action_dispatch/middleware/callbacks.rb:27:in `block in call'
activesupport (7.0.3.1) lib/active_support/callbacks.rb:99:in `run_callbacks'
actionpack (7.0.3.1) lib/action_dispatch/middleware/callbacks.rb:26:in `call'
actionpack (7.0.3.1) lib/action_dispatch/middleware/debug_exceptions.rb:28:in `call'
actionpack (7.0.3.1) lib/action_dispatch/middleware/show_exceptions.rb:26:in `call'
logster (2.11.3) lib/logster/middleware/reporter.rb:43:in `call'
railties (7.0.3.1) lib/rails/rack/logger.rb:40:in `call_app'
railties (7.0.3.1) lib/rails/rack/logger.rb:27:in `call'
config/initializers/100-quiet_logger.rb:23:in `call'
config/initializers/100-silence_logger.rb:31:in `call'
actionpack (7.0.3.1) lib/action_dispatch/middleware/remote_ip.rb:93:in `call'
actionpack (7.0.3.1) lib/action_dispatch/middleware/request_id.rb:26:in `call'
lib/middleware/enforce_hostname.rb:23:in `call'
rack (2.2.4) lib/rack/method_override.rb:24:in `call'
actionpack (7.0.3.1) lib/action_dispatch/middleware/executor.rb:14:in `call'
rack (2.2.4) lib/rack/sendfile.rb:110:in `call'
actionpack (7.0.3.1) lib/action_dispatch/middleware/host_authorization.rb:131:in `call'
rack-mini-profiler (3.0.0) lib/mini_profiler/profiler.rb:249:in `call'


message_bus (4.2.0) lib/message_bus/rack/middleware.rb:60:in `call'
lib/middleware/request_tracker.rb:202:in `call'
railties (7.0.3.1) lib/rails/engine.rb:530:in `call'
railties (7.0.3.1) lib/rails/railtie.rb:226:in `public_send'
railties (7.0.3.1) lib/rails/railtie.rb:226:in `method_missing'
rack (2.2.4) lib/rack/urlmap.rb:74:in `block in call'
rack (2.2.4) lib/rack/urlmap.rb:58:in `each'
rack (2.2.4) lib/rack/urlmap.rb:58:in `call'
unicorn (6.1.0) lib/unicorn/http_server.rb:634:in `process_client'
unicorn (6.1.0) lib/unicorn/http_server.rb:739:in `worker_loop'
unicorn (6.1.0) lib/unicorn/http_server.rb:547:in `spawn_missing_workers'
unicorn (6.1.0) lib/unicorn/http_server.rb:143:in `start'
unicorn (6.1.0) bin/unicorn:128:in `<top (required)>'
vendor/bundle/ruby/2.7.0/bin/unicorn:25:in `load'
vendor/bundle/ruby/2.7.0/bin/unicorn:25:in `<main>'

That looks like a bug in the discourse-question-answer plugin. I think if you remove that plugin (or perhaps use safe mode) that error will go away.