Just updated from 2.5 to 3.0.1, following the upgrade instructions in the manual. However, when running foreman-rake, or starting the foreman service, I get errors like the one in the subject. Here's a stacktrace:

Dez 09 08:17:41 he-puppet foreman[3225]: => Run `rails server --help` for more startup options
Dez 09 08:17:43 he-puppet foreman[3225]: /usr/share/foreman/vendor/ruby/2.5.0/gems/foreman_puppet-0.0.2/lib/foreman_puppet/register.rb:141: warning: already initialized constant Foreman::Plugin::RbacSupport::AUTO_EXTENDED_ROLES
Dez 09 08:17:43 he-puppet foreman[3225]: /usr/share/foreman/app/registries/foreman/plugin/rbac_support.rb:5: warning: previous definition of AUTO_EXTENDED_ROLES was here
Dez 09 08:17:43 he-puppet foreman[3225]: Exiting
Dez 09 08:17:43 he-puppet foreman[3225]: /usr/share/foreman/vendor/ruby/2.5.0/gems/foreman_puppet-0.0.2/app/models/concerns/foreman_puppet/extensions/hostgroup.rb:12:in `instance_variable_set': can't modify frozen NilClass (FrozenError)
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/foreman_puppet-0.0.2/app/models/concerns/foreman_puppet/extensions/hostgroup.rb:12:in `block in <module:Hostgroup>'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/concern.rb:122:in `class_eval'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/concern.rb:122:in `append_features'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/foreman_puppet-0.0.2/lib/foreman_puppet/engine.rb:36:in `include'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/foreman_puppet-0.0.2/lib/foreman_puppet/engine.rb:36:in `block in <class:Engine>'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/callbacks.rb:428:in `instance_exec'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/callbacks.rb:428:in `block in make_lambda'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/callbacks.rb:200:in `block (2 levels) in halting'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/callbacks.rb:605:in `block (2 levels) in default_terminator'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/callbacks.rb:604:in `catch'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/callbacks.rb:604:in `block in default_terminator'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/callbacks.rb:201:in `block in halting'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/callbacks.rb:513:in `block in invoke_before'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/callbacks.rb:513:in `each'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/callbacks.rb:513:in `invoke_before'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/callbacks.rb:134:in `run_callbacks'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/reloader.rb:88:in `prepare!'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/application/finisher.rb:113:in `block in <module:Finisher>'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/initializable.rb:32:in `instance_exec'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/initializable.rb:32:in `run'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/config/initializers/0_print_time_spent.rb:45:in `block in run'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/config/initializers/0_print_time_spent.rb:17:in `benchmark'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/config/initializers/0_print_time_spent.rb:45:in `run'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/initializable.rb:61:in `block in run_initializers'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/lib/ruby/2.5.0/tsort.rb:228:in `block in tsort_each'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/lib/ruby/2.5.0/tsort.rb:350:in `block (2 levels) in each_strongly_connected_component'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/lib/ruby/2.5.0/tsort.rb:431:in `each_strongly_connected_component_from'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/lib/ruby/2.5.0/tsort.rb:349:in `block in each_strongly_connected_component'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/lib/ruby/2.5.0/tsort.rb:347:in `each'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/lib/ruby/2.5.0/tsort.rb:347:in `call'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/lib/ruby/2.5.0/tsort.rb:347:in `each_strongly_connected_component'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/lib/ruby/2.5.0/tsort.rb:226:in `tsort_each'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/lib/ruby/2.5.0/tsort.rb:205:in `tsort_each'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/initializable.rb:60:in `run_initializers'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/application.rb:363:in `initialize!'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/railtie.rb:190:in `public_send'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/railtie.rb:190:in `method_missing'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/config/environment.rb:5:in `<top (required)>'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/dependencies.rb:324:in `require'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/dependencies.rb:324:in `block in require'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/dependencies.rb:291:in `load_dependency'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/dependencies.rb:324:in `require'
Dez 09 08:17:43 he-puppet foreman[3225]:         from config.ru:5:in `block in <main>'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/rack-2.2.3/lib/rack/builder.rb:116:in `eval'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/rack-2.2.3/lib/rack/builder.rb:116:in `new_from_string'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/rack-2.2.3/lib/rack/builder.rb:105:in `load_file'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/rack-2.2.3/lib/rack/builder.rb:66:in `parse_file'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/rack-2.2.3/lib/rack/server.rb:349:in `build_app_and_options_from_config'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/rack-2.2.3/lib/rack/server.rb:249:in `app'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/rack-2.2.3/lib/rack/server.rb:422:in `wrapped_app'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/rack-2.2.3/lib/rack/server.rb:312:in `block in start'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/rack-2.2.3/lib/rack/server.rb:379:in `handle_profiling'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/rack-2.2.3/lib/rack/server.rb:311:in `start'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/commands/server/server_command.rb:39:in `start'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/commands/server/server_command.rb:147:in `block in perform'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/commands/server/server_command.rb:138:in `tap'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/commands/server/server_command.rb:138:in `perform'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/thor-1.1.0/lib/thor/command.rb:27:in `run'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/thor-1.1.0/lib/thor/invocation.rb:127:in `invoke_command'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/thor-1.1.0/lib/thor.rb:392:in `dispatch'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/command/base.rb:69:in `perform'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/command.rb:46:in `invoke'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/railties-6.0.3.7/lib/rails/commands.rb:18:in `<top (required)>'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/dependencies.rb:324:in `require'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/dependencies.rb:324:in `block in require'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/dependencies.rb:291:in `load_dependency'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/vendor/ruby/2.5.0/gems/activesupport-6.0.3.7/lib/active_support/dependencies.rb:324:in `require'
Dez 09 08:17:43 he-puppet foreman[3225]:         from /usr/share/foreman/bin/rails:9:in `<main>'
Dez 09 08:17:43 he-puppet systemd[1]: foreman.service: Main process exited, code=exited, status=1/FAILURE

Versions:

# dpkg --list|awk '/(puppet|foreman)/ {print $2" "$3}'
foreman 3.0.1-2
foreman-debug 3.0.1-2
foreman-journald 3.0.1-2
foreman-postgresql 3.0.1-2
foreman-proxy 3.0.1-1
foreman-service 3.0.1-2
puppet-agent 6.25.1-1buster
puppet6-release 6.0.0-14buster
puppetdb 6.19.1-1buster
puppetdb-termini 6.19.1-1buster
puppetserver 6.17.1-1buster
ruby-foreman-puppet 0.0.2-1