title: No light as to how to trace this error on a migration to Rails 5
body: <p>I've been migrating a legacy app into newer versions of rails. The issue I have now is that I come up with this error when I try to bring the console up:</p>
  <pre><code>$ rails c
  /home/user/.rvm/gems/ruby-2.3.3/gems/actionpack-5.2.5/lib/action_dispatch/middleware/stack.rb:108:in `assert_index': No such middleware to insert after: &quot;ActionDispatch::DebugExceptions&quot; (RuntimeError)
      from /home/user/.rvm/gems/ruby-2.3.3/gems/actionpack-5.2.5/lib/action_dispatch/middleware/stack.rb:82:in `insert_after'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/configuration.rb:71:in `block in merge_into'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/configuration.rb:70:in `each'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/configuration.rb:70:in `merge_into'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/engine.rb:509:in `block in app'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/engine.rb:506:in `synchronize'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/engine.rb:506:in `app'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/application/finisher.rb:47:in `block in &lt;module:Finisher&gt;'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/initializable.rb:32:in `instance_exec'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/initializable.rb:32:in `run'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/initializable.rb:61:in `block in run_initializers'
      from /usr/share/rvm/rubies/ruby-2.3.3/lib/ruby/2.3.0/tsort.rb:228:in `block in tsort_each'
      from /usr/share/rvm/rubies/ruby-2.3.3/lib/ruby/2.3.0/tsort.rb:350:in `block (2 levels) in each_strongly_connected_component'
      from /usr/share/rvm/rubies/ruby-2.3.3/lib/ruby/2.3.0/tsort.rb:431:in `each_strongly_connected_component_from'
      from /usr/share/rvm/rubies/ruby-2.3.3/lib/ruby/2.3.0/tsort.rb:349:in `block in each_strongly_connected_component'
      from /usr/share/rvm/rubies/ruby-2.3.3/lib/ruby/2.3.0/tsort.rb:347:in `each'
      from /usr/share/rvm/rubies/ruby-2.3.3/lib/ruby/2.3.0/tsort.rb:347:in `call'
      from /usr/share/rvm/rubies/ruby-2.3.3/lib/ruby/2.3.0/tsort.rb:347:in `each_strongly_connected_component'
      from /usr/share/rvm/rubies/ruby-2.3.3/lib/ruby/2.3.0/tsort.rb:226:in `tsort_each'
      from /usr/share/rvm/rubies/ruby-2.3.3/lib/ruby/2.3.0/tsort.rb:205:in `tsort_each'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/initializable.rb:60:in `run_initializers'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/application.rb:361:in `initialize!'
      from /home/user/Projects/firelight/firelight/config/environment.rb:5:in `&lt;main&gt;'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/bootsnap-1.7.3/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `require'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/bootsnap-1.7.3/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `block in require_with_bootsnap_lfi'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/bootsnap-1.7.3/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/bootsnap-1.7.3/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require_with_bootsnap_lfi'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/bootsnap-1.7.3/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in `require'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/activesupport-5.2.5/lib/active_support/dependencies.rb:291:in `block in require'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/activesupport-5.2.5/lib/active_support/dependencies.rb:257:in `load_dependency'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/activesupport-5.2.5/lib/active_support/dependencies.rb:291:in `require'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/application.rb:337:in `require_environment!'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/command/actions.rb:28:in `require_environment!'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/command/actions.rb:15:in `require_application_and_environment!'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/commands/console/console_command.rb:95:in `perform'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/thor-1.1.0/lib/thor/command.rb:27:in `run'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/thor-1.1.0/lib/thor/invocation.rb:127:in `invoke_command'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/thor-1.1.0/lib/thor.rb:392:in `dispatch'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/command/base.rb:69:in `perform'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/command.rb:46:in `invoke'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/railties-5.2.5/lib/rails/commands.rb:18:in `&lt;main&gt;'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/bootsnap-1.7.3/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `require'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/bootsnap-1.7.3/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in `block in require_with_bootsnap_lfi'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/bootsnap-1.7.3/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/bootsnap-1.7.3/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require_with_bootsnap_lfi'
      from /home/user/.rvm/gems/ruby-2.3.3/gems/bootsnap-1.7.3/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in `require'
      from bin/rails:4:in `&lt;main&gt;'
  </code></pre>
  <p>I'm using Rails 5.2.5 with ruby 2.3.3 for now.
  The error stacktrace isn't telling me anything significant at least nothing that I can determine.</p>
  <p>Could I kindly get some pointers as to where can a good place to look be?</p>
  <p>Edit: I linked to a post that has an answer to this. Basically if this error happens a good way is to look at the gems to see if there is a specific gem that needs to be upgraded.</p>