Upgrade from Ruby 2.1.4 & Rails 4.1.8 to Ruby 2.1.5 & Rails 4.2.0 raise undefined method 'simplified_type'

[axcr]

upgrading my app ruby & rails raise exception during local testing (rails s).

i've upgrade my app from ruby 2.1.4, rails 4.1.8 and psql (9.3.5)
to ruby 2.1.5, rails 4.2.0 and same psql version and following happens:

xxxxx$ rails s
=> Booting Puma
=> Rails 4.2.0 application starting in development on http://localhost:3000
=> Run rails server -h for more startup options
=> Ctrl-C to shutdown server
Exiting
/Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/core_ext/module/aliasing.rb:32:in alias_method': undefined methodsimplified_type' for class ActiveRecord::ConnectionAdapters::PostgreSQLColumn' (NameError) from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/core_ext/module/aliasing.rb:32:inalias_method_chain'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activerecord-postgres-hstore-0.7.7/lib/activerecord-postgres-hstore/activerecord.rb:80:in <class:PostgreSQLColumn>' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activerecord-postgres-hstore-0.7.7/lib/activerecord-postgres-hstore/activerecord.rb:74:inmodule:ConnectionAdapters'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activerecord-postgres-hstore-0.7.7/lib/activerecord-postgres-hstore/activerecord.rb:70:in <module:ActiveRecord>' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activerecord-postgres-hstore-0.7.7/lib/activerecord-postgres-hstore/activerecord.rb:2:in<top (required)>'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/dependencies.rb:274:in require' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/dependencies.rb:274:inblock in require'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/dependencies.rb:240:in load_dependency' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/dependencies.rb:274:inrequire'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activerecord-postgres-hstore-0.7.7/lib/activerecord-postgres-hstore/railties.rb:18:in block (2 levels) in <class:Hstore>' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/lazy_load_hooks.rb:38:ininstance_eval'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/lazy_load_hooks.rb:38:in execute_hook' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/lazy_load_hooks.rb:28:inblock in on_load'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/lazy_load_hooks.rb:27:in each' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/lazy_load_hooks.rb:27:inon_load'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activerecord-postgres-hstore-0.7.7/lib/activerecord-postgres-hstore/railties.rb:17:in block in <class:Hstore>' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/initializable.rb:30:ininstance_exec'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/initializable.rb:30:in run' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/initializable.rb:55:inblock in run_initializers'
from /Users/xxxxx/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/tsort.rb:226:in block in tsort_each' from /Users/xxxxx/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/tsort.rb:348:inblock (2 levels) in each_strongly_connected_component'
from /Users/xxxxx/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/tsort.rb:427:in each_strongly_connected_component_from' from /Users/xxxxx/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/tsort.rb:347:inblock in each_strongly_connected_component'
from /Users/xxxxx/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/tsort.rb:345:in each' from /Users/xxxxx/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/tsort.rb:345:incall'
from /Users/xxxxx/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/tsort.rb:345:in each_strongly_connected_component' from /Users/xxxxx/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/tsort.rb:224:intsort_each'
from /Users/xxxxx/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/tsort.rb:205:in tsort_each' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/initializable.rb:54:inrun_initializers'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/application.rb:352:in initialize!' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/railtie.rb:194:inpublic_send'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/railtie.rb:194:in method_missing' from /Users/xxxxx/Projects/Apps/xxxxx/config/environment.rb:5:in<top (required)>'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/dependencies.rb:274:in require' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/dependencies.rb:274:inblock in require'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/dependencies.rb:240:in load_dependency' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/activesupport-4.2.0/lib/active_support/dependencies.rb:274:inrequire'
from /Users/xxxxx/Projects/Apps/xxxxx/config.ru:3:in block in <main>' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/rack-1.6.0/lib/rack/builder.rb:55:ininstance_eval'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/rack-1.6.0/lib/rack/builder.rb:55:in initialize' from /Users/xxxxx/Projects/Apps/xxxxx/config.ru:innew'
from /Users/xxxxx/Projects/Apps/xxxxx/config.ru:in <main>' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/rack-1.6.0/lib/rack/builder.rb:49:ineval'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/rack-1.6.0/lib/rack/builder.rb:49:in new_from_string' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/rack-1.6.0/lib/rack/builder.rb:40:inparse_file'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/rack-1.6.0/lib/rack/server.rb:299:in build_app_and_options_from_config' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/rack-1.6.0/lib/rack/server.rb:208:inapp'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/commands/server.rb:61:in app' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/rack-1.6.0/lib/rack/server.rb:336:inwrapped_app'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/commands/server.rb:139:in log_to_stdout' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/commands/server.rb:78:instart'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:80:in block in server' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:75:intap'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:75:in server' from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:39:inrun_command!'
from /Users/xxxxx/.rvm/gems/ruby-2.1.5/gems/railties-4.2.0/lib/rails/commands.rb:17:in <top (required)>' from bin/rails:4:inrequire'
from bin/rails:4:in `

'

what i'm doing wrong here?
thx!

[rafaelfranca]

From the stack trace it seems to be a problem at activerecord-postgres-hstore gem patching Rails internals.

[chibicode]

@axcr @rafaelfranca re-raised an issue here: diogob/activerecord-postgres-hstore#127