I started to work as a junior Rails developer and my first task is to update a legacy Rails 2.3.8 app written around 2008 in Jruby 1.5.3 (Ruby 1.8.7) to Rails 5.1.2 in Jruby 9.1.12 (Ruby 2.3.3). It consists of 222 controllers and 122 models, and only spits XML that is consumed by a Java Swing desktop app. Searching I found that the best way to do it, is step by step from one minor version to another correcting all issues in the inter. I reached version 3.0.12 in two weeks leaving the aplication without warnings, but I was asked to go directly to Jruby 9.X.X and Rails 5.1.X. With a few difficulties I get the server up, but when I try to login in the application I got this error. I suspect about the jdbc adapter gem, but any gem below 5.0pre1 works with Rails 5. Could this be only a parsing error from the DB? Should I continue with the cycle I was carrying?
NOTE: There's no test suite for the app, and there are eight modules that override some Rails core methods.
Started POST "/login/login_xml" for 127.0.0.1 at 2017-08-03 12:21:03 -0500
ActiveRecord::SchemaMigration Load (0.0ms) SELECT `schema_migrations`.*
FROM `schema_migrations`
NoMethodError (undefined method `to_sym' for nil:NilClass
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activerecord (5.0.4) lib/active_record/attribute_methods/time_zone_conversion.rb:88:in `create_time_zone_conversion_attribute?'
activerecord (5.0.4) lib/active_record/attribute_methods/time_zone_conversion.rb:78:in `block in inherited'
activerecord (5.0.4) lib/active_record/attribute_decorators.rb:62:in `block in matching'
org/jruby/RubyArray.java:2565:in `select'
activerecord (5.0.4) lib/active_record/attribute_decorators.rb:61:in `matching'
activerecord (5.0.4) lib/active_record/attribute_decorators.rb:57:in `decorators_for'
activerecord (5.0.4) lib/active_record/attribute_decorators.rb:48:in `apply'
activerecord (5.0.4) lib/active_record/attribute_decorators.rb:30:in `block in load_schema!'
org/jruby/RubyHash.java:1343:in `each'
activerecord (5.0.4) lib/active_record/attribute_decorators.rb:29:in `load_schema!'
activerecord (5.0.4) lib/active_record/model_schema.rb:455:in `block in load_schema'
C:/jruby-9.1.12.0/lib/ruby/stdlib/monitor.rb:214:in `mon_synchronize'
activerecord (5.0.4) lib/active_record/model_schema.rb:452:in `load_schema'
activerecord (5.0.4) lib/active_record/model_schema.rb:343:in `columns_hash'
activerecord (5.0.4) lib/active_record/querying.rb:41:in `find_by_sql'
activerecord (5.0.4) lib/active_record/relation.rb:702:in `exec_queries'
activerecord (5.0.4) lib/active_record/relation.rb:583:in `load'
activerecord (5.0.4) lib/active_record/relation.rb:260:in `records'
activerecord (5.0.4) lib/active_record/relation/delegation.rb:38:in `map'
activerecord (5.0.4) lib/active_record/migration.rb:1031:in `block in get_all_versions'
activesupport (5.0.4) lib/active_support/deprecation/reporting.rb:36:in `silence'
activesupport (5.0.4) lib/active_support/deprecation/instance_delegator.rb:20:in `silence'
activerecord (5.0.4) lib/active_record/migration.rb:1029:in `get_all_versions'
activerecord (5.0.4) lib/active_record/migration.rb:1043:in `needs_migration?'
activerecord (5.0.4) lib/active_record/migration.rb:573:in `check_pending!'
activerecord (5.0.4) lib/active_record/migration.rb:549:in `call'
actionpack (5.0.4) lib/action_dispatch/middleware/callbacks.rb:38:in `block in call'
activesupport (5.0.4) lib/active_support/callbacks.rb:97:in `__run_callbacks__'
activesupport (5.0.4) lib/active_support/callbacks.rb:750:in `_run_call_callbacks'
activesupport (5.0.4) lib/active_support/callbacks.rb:90:in `run_callbacks'
actionpack (5.0.4) lib/action_dispatch/middleware/callbacks.rb:36:in `call'
actionpack (5.0.4) lib/action_dispatch/middleware/executor.rb:12:in `call'
actionpack (5.0.4) lib/action_dispatch/middleware/remote_ip.rb:79:in `call'
actionpack (5.0.4) lib/action_dispatch/middleware/debug_exceptions.rb:49:in `call'
actionpack (5.0.4) lib/action_dispatch/middleware/show_exceptions.rb:31:in `call'
railties (5.0.4) lib/rails/rack/logger.rb:36:in `call_app'
railties (5.0.4) lib/rails/rack/logger.rb:24:in `block in call'
activesupport (5.0.4) lib/active_support/tagged_logging.rb:69:in `block in tagged'
activesupport (5.0.4) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (5.0.4) lib/active_support/tagged_logging.rb:69:in `tagged'
railties (5.0.4) lib/rails/rack/logger.rb:24:in `call'
sprockets-rails (3.2.0) lib/sprockets/rails/quiet_assets.rb:13:in `call'
actionpack (5.0.4) lib/action_dispatch/middleware/request_id.rb:24:in `call'
rack (2.0.3) lib/rack/method_override.rb:22:in `call'
rack (2.0.3) lib/rack/runtime.rb:22:in `call'
activesupport (5.0.4) lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call'
actionpack (5.0.4) lib/action_dispatch/middleware/executor.rb:12:in `call'
actionpack (5.0.4) lib/action_dispatch/middleware/static.rb:136:in `call'
rack (2.0.3) lib/rack/sendfile.rb:111:in `call'
railties (5.0.4) lib/rails/engine.rb:522:in `call'
puma-3.9.1 (java) lib/puma/configuration.rb:224:in `call'
puma-3.9.1 (java) lib/puma/server.rb:602:in `handle_request'
puma-3.9.1 (java) lib/puma/server.rb:435:in `process_client'
puma-3.9.1 (java) lib/puma/server.rb:299:in `block in run'
puma-3.9.1 (java) lib/puma/thread_pool.rb:120:in `block in spawn_thread'
Rendering C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/diagnostics.html.erb within rescues/layout
Rendering C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/_source.html.erb
Rendered C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/_source.html.erb (16.0ms)
Rendering C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb
Rendered C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb (16.0ms)
Rendering C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb
Rendered C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb (12.0ms)
Rendered C:/jruby-9.1.12.0/lib/ruby/gems/shared/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/diagnostics.html.erb within rescues/layout (142.0ms)
The simplest answer is that you need to immediately push back on the request to skip directly to 5.1. You are being set up for failure. It may not even be possible to go from your current version to 5.1, and without digging into your project and analyzing the gems you're currently reliant on, there's no way to know.
You are trying to take an extremely dated project to a modern version and that is simply going to take a significant amount of time to do properly. This is why yearly/bi-yearly updates to modern versions are important, so you don't accumulate such high levels of technical debt.
Please talk with a higher-level dev or your manager about this unreasonable request.