Question post on collab.codidact.org that is blocked by cloudfare

gistfile1.txt

title of question: How to fix 500 Server Error "NoMethodError: undefined method `id' for nil:NilClass"?
tags: support, installation
body content:

Following the [set up guide](https://collab.codidact.org/posts/280451/280452#answer-280452) I was able to start rails server and got my very first QPixel page served (see screenshot):

![Screenshot of the 500 Server Error](https://collab.codidact.org/uploads/nTMMK32Yu5C8JtMYJYxaUbEN)

Unfortunately it was a `500 Server Error`, which I did not expect and which wasn't mentioned in the guide. Attached is part of the console output which speaks of a `NoMethodError (undefined method `id' for nil:NilClass)`.

```
Started GET "/" for 127.0.0.1 at 2022-01-06 09:55:55 +0100
   (1.6ms)  SET NAMES utf8mb4 COLLATE utf8mb4_unicode_ci,  @@SESSION.sql_mode = CONCAT(CONCAT(@@sql_mode, ',STRICT_ALL_TABLES'), ',NO_AUTO_VALUE_ON_ZERO'),  @@SESSION.sql_auto_is_null = 0, @@SESSION.wait_timeout = 2147483
   (4.3ms)  SELECT `schema_migrations`.`version` FROM `schema_migrations` ORDER BY `schema_migrations`.`version` ASC
Processing by CategoriesController#homepage as HTML
/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activemodel-5.2.6/lib/active_model/type/integer.rb:13: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activemodel-5.2.6/lib/active_model/type/value.rb:8: warning: The called method `initialize' is defined here
/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activerecord-5.2.6/lib/active_record/connection_adapters/mysql/database_statements.rb:12: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activerecord-5.2.6/lib/active_record/connection_adapters/abstract/query_cache.rb:95: warning: The called method `select_all' is defined here
  Community Load (20.8ms)  SELECT  `communities`.* FROM `communities` WHERE `communities`.`host` = 'localhost:3000' LIMIT 1
  Host localhost:3000, community #1 (Dev Community)
  User Load (9.0ms)  SELECT  `users`.* FROM `users` WHERE `users`.`id` = 1 ORDER BY `users`.`id` ASC LIMIT 1
/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activerecord-5.2.6/lib/active_record/relation/delegation.rb:132: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activerecord-5.2.6/lib/active_record/relation.rb:25: warning: The called method `initialize' is defined here
  CommunityUser Load (1.5ms)  SELECT  `community_users`.* FROM `community_users` WHERE `community_users`.`user_id` = 1 AND `community_users`.`community_id` = 1 LIMIT 1
  User 1 (aaa) signed in
/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activerecord-5.2.6/lib/active_record/associations.rb:1855: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activerecord-5.2.6/lib/active_record/associations.rb:1368: warning: The called method `has_many' is defined here
  PostType Load (2.4ms)  SELECT  `post_types`.* FROM `post_types` ORDER BY `post_types`.`id` ASC LIMIT 1000
   (3.1ms)  SELECT COUNT(*) FROM `flags` WHERE `flags`.`community_id` = 1 AND `flags`.`status` IS NULL
  ModWarning Exists (1.3ms)  SELECT  1 AS one FROM `warnings` WHERE `warnings`.`community_user_id` = 1 AND `warnings`.`active` = TRUE LIMIT 1
  Category Load (1.6ms)  SELECT  `categories`.* FROM `categories` WHERE `categories`.`community_id` = 1 AND `categories`.`is_homepage` = TRUE ORDER BY `categories`.`id` ASC LIMIT 1
Completed 500 Internal Server Error in 199ms (ActiveRecord: 66.8ms)



NoMethodError (undefined method `id' for nil:NilClass):

app/controllers/categories_controller.rb:171:in `update_last_visit'
app/controllers/categories_controller.rb:24:in `homepage'
Processing by ErrorsController#error as HTML
  Host localhost:3000, community #1 (Dev Community)
  User 1 (aaa) signed in
  CACHE  (0.0ms)  SELECT COUNT(*) FROM `flags` WHERE `flags`.`community_id` = 1 AND `flags`.`status` IS NULL
  CACHE ModWarning Exists (0.0ms)  SELECT  1 AS one FROM `warnings` WHERE `warnings`.`community_user_id` = 1 AND `warnings`.`active` = TRUE LIMIT 1
/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activerecord-5.2.6/lib/active_record/transactions.rb:212: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activerecord-5.2.6/lib/active_record/connection_adapters/abstract/database_statements.rb:260: warning: The called method `transaction' is defined here
/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activerecord-5.2.6/lib/active_record/connection_adapters/abstract/transaction.rb:171: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activerecord-5.2.6/lib/active_record/connection_adapters/abstract/transaction.rb:97: warning: The called method `initialize' is defined here
   (0.6ms)  BEGIN
  ErrorLog Create (3.9ms)  INSERT INTO `error_logs` (`community_id`, `user_id`, `klass`, `message`, `backtrace`, `request_uri`, `host`, `created_at`, `updated_at`, `uuid`, `user_agent`) VALUES (1, 1, 'NoMethodError', 'undefined method `id\' for nil:NilClass', '/home/abanta/qpixel/app/controllers/categories_controller.rb:171:in `update_last_visit\'\n/home/abanta/qpixel/app/controllers/categories_controller.rb:24:in `homepage\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_controller/metal/basic_implicit_render.rb:6:in `send_action\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/abstract_controller/base.rb:194:in `process_action\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_controller/metal/rendering.rb:30:in `process_action\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/abstract_controller/callbacks.rb:42:in `block in process_action\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activesupport-5.2.6/lib/active_support/callbacks.rb:132:in `run_callbacks\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/abstract_controller/callbacks.rb:41:in `process_action\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_controller/metal/rescue.rb:22:in `process_action\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_controller/metal/instrumentation.rb:34:in `block in process_action\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activesupport-5.2.6/lib/active_support/notifications.rb:168:in `block in instrument\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activesupport-5.2.6/lib/active_support/notifications/instrumenter.rb:23:in `instrument\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activesupport-5.2.6/lib/active_support/notifications.rb:168:in `instrument\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_controller/metal/instrumentation.rb:32:in `process_action\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_controller/metal/params_wrapper.rb:256:in `process_action\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activerecord-5.2.6/lib/active_record/railties/controller_runtime.rb:24:in `process_action\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/abstract_controller/base.rb:134:in `process\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionview-5.2.6/lib/action_view/rendering.rb:32:in `process\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_controller/metal.rb:191:in `dispatch\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_controller/metal.rb:252:in `dispatch\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/routing/route_set.rb:52:in `dispatch\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/routing/route_set.rb:34:in `serve\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/journey/router.rb:52:in `block in serve\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/journey/router.rb:35:in `each\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/journey/router.rb:35:in `serve\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/routing/route_set.rb:840:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/warden-1.2.9/lib/warden/manager.rb:36:in `block in call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/warden-1.2.9/lib/warden/manager.rb:34:in `catch\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/warden-1.2.9/lib/warden/manager.rb:34:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/rack-2.2.3/lib/rack/tempfile_reaper.rb:15:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/rack-2.2.3/lib/rack/etag.rb:27:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/rack-2.2.3/lib/rack/conditional_get.rb:27:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/rack-2.2.3/lib/rack/head.rb:12:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/http/content_security_policy.rb:18:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/rack-2.2.3/lib/rack/session/abstract/id.rb:266:in `context\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/rack-2.2.3/lib/rack/session/abstract/id.rb:260:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/middleware/cookies.rb:670:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activerecord-5.2.6/lib/active_record/migration.rb:559:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/middleware/callbacks.rb:28:in `block in call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activesupport-5.2.6/lib/active_support/callbacks.rb:98:in `run_callbacks\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/middleware/callbacks.rb:26:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/middleware/executor.rb:14:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/middleware/debug_exceptions.rb:61:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/web-console-3.7.0/lib/web_console/middleware.rb:135:in `call_app\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/web-console-3.7.0/lib/web_console/middleware.rb:30:in `block in call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/web-console-3.7.0/lib/web_console/middleware.rb:20:in `catch\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/web-console-3.7.0/lib/web_console/middleware.rb:20:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/middleware/show_exceptions.rb:33:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/railties-5.2.6/lib/rails/rack/logger.rb:38:in `call_app\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/railties-5.2.6/lib/rails/rack/logger.rb:26:in `block in call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activesupport-5.2.6/lib/active_support/tagged_logging.rb:71:in `block in tagged\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activesupport-5.2.6/lib/active_support/tagged_logging.rb:28:in `tagged\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activesupport-5.2.6/lib/active_support/tagged_logging.rb:71:in `tagged\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/railties-5.2.6/lib/rails/rack/logger.rb:26:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/middleware/remote_ip.rb:81:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/middleware/request_id.rb:27:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/rack-2.2.3/lib/rack/method_override.rb:24:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/rack-2.2.3/lib/rack/runtime.rb:22:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/activesupport-5.2.6/lib/active_support/cache/strategy/local_cache_middleware.rb:29:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/middleware/executor.rb:14:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/actionpack-5.2.6/lib/action_dispatch/middleware/static.rb:127:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/rack-2.2.3/lib/rack/sendfile.rb:110:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/rack-mini-profiler-2.3.2/lib/mini_profiler/profiler.rb:384:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/railties-5.2.6/lib/rails/engine.rb:524:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/puma-4.3.10/lib/puma/configuration.rb:228:in `call\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/puma-4.3.10/lib/puma/server.rb:718:in `handle_request\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/puma-4.3.10/lib/puma/server.rb:472:in `process_client\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/puma-4.3.10/lib/puma/server.rb:328:in `block in run\'\n/home/abanta/qpixel/vendor/bundle/ruby/2.7.0/gems/puma-4.3.10/lib/puma/thread_pool.rb:134:in `block in spawn_thread\'', 'http://localhost:3000/', 'localhost:3000', '2022-01-06 08:55:56', '2022-01-06 08:55:56', 'a376286a-d0c0-4cc0-8532-16c8f630b2ca', 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:95.0) Gecko/20100101 Firefox/95.0')
   (3.7ms)  COMMIT
  Rendering errors/internal_server_error.html.erb within layouts/without_sidebar
  Rendered errors/internal_server_error.html.erb within layouts/without_sidebar (1.4ms)
  SiteSetting Load (1.5ms)  SELECT  `site_settings`.* FROM `site_settings` WHERE (`site_settings`.`community_id` = 1 OR `site_settings`.`community_id` IS NULL) AND `site_settings`.`name` = 'IconPath' ORDER BY IF(site_settings.community_id IS NULL, 1, 0) LIMIT 1
  Rendered layouts/_head.html.erb (359.5ms)
  SiteSetting Load (0.9ms)  SELECT  `site_settings`.* FROM `site_settings` WHERE (`site_settings`.`community_id` = 1 OR `site_settings`.`community_id` IS NULL) AND `site_settings`.`name` = 'MobileLogoPath' ORDER BY IF(site_settings.community_id IS NULL, 1, 0) LIMIT 1
   (1.1ms)  SELECT COUNT(*) FROM `notifications` WHERE `notifications`.`user_id` = 1 AND `notifications`.`is_read` = FALSE
  ActiveStorage::Attachment Load (1.7ms)  SELECT  `active_storage_attachments`.* FROM `active_storage_attachments` WHERE `active_storage_attachments`.`record_id` = 1 AND `active_storage_attachments`.`record_type` = 'User' AND `active_storage_attachments`.`name` = 'avatar' LIMIT 1
  Community Load (0.8ms)  SELECT `communities`.* FROM `communities` WHERE `communities`.`is_fake` = FALSE
  Community Load (0.8ms)  SELECT `communities`.* FROM `communities` WHERE `communities`.`is_fake` = FALSE AND `communities`.`hidden` = FALSE
  Category Load (0.9ms)  SELECT `categories`.* FROM `categories` WHERE `categories`.`community_id` = 1 ORDER BY `categories`.`sequence` ASC, `categories`.`id` ASC
  Rendered layouts/_header.html.erb (26.4ms)
  Rendered layouts/_footer.html.erb (0.6ms)
  SiteSetting Load (0.8ms)  SELECT  `site_settings`.* FROM `site_settings` WHERE (`site_settings`.`community_id` = 1 OR `site_settings`.`community_id` IS NULL) AND `site_settings`.`name` = 'AnalyticsURL' ORDER BY IF(site_settings.community_id IS NULL, 1, 0) LIMIT 1
  Rendered layouts/_matomo.html.erb (3.0ms)
Completed 500 Internal Server Error in 429ms (Views: 382.4ms | ActiveRecord: 25.4ms)

...

Completed 500 Internal Server Error in 360ms (Views: 204.1ms | ActiveRecord: 26.5ms)
```

Is this intended behavior or a bug (and if so how to fix it)?

I tried to continue with the guide and signed up a user, but that didn't change anything about the error. It seems like the dev community is not set up correctly.

In trying to reach this point I repeated steps of the manual several times (and encountered other errors), so maybe I compromised the state of the installation somewhere. I will repeat the guide on a clean system again to be sure. Nevertheless this question should remain as something that might happen to others as well.