我很头疼试图弄清楚这一点。每次我尝试将我的应用程序部署到生产中时，我都会收到此错误：
/Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/core/service_interface.rb:24:in `module_eval': undefined method `each' for nil:NilClass (NoMethodError)
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/client/xml.rb:29:in `<module:XML>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/client/xml.rb:19:in `<class:Client>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/client/xml.rb:16:in `<class:SimpleEmailService>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/client/xml.rb:15:in `<module:AWS>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/client/xml.rb:14:in `<top (required)>'
from (eval):1:in `configure_client'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/core/client.rb:484:in `module_eval'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/core/client.rb:484:in `configure_client'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/core/configured_client_methods.rb:27:in `configure_client'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/client.rb:32:in `<class:Client>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/client.rb:18:in `<class:SimpleEmailService>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/client.rb:15:in `<module:AWS>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/client.rb:14:in `<top (required)>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/errors.rb:20:in `<module:Errors>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/errors.rb:18:in `<class:SimpleEmailService>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/errors.rb:15:in `<module:AWS>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service/errors.rb:14:in `<top (required)>'
from (eval):1:in `included'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/core/service_interface.rb:24:in `module_eval'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/core/service_interface.rb:24:in `included'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service.rb:146:in `include'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service.rb:146:in `<class:SimpleEmailService>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service.rb:136:in `<module:AWS>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/simple_email_service.rb:17:in `<top (required)>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/aws-sdk-1.3.9/lib/aws/rails.rb:157:in `block in add_action_mailer_delivery_method'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/lazy_load_hooks.rb:36:in `instance_eval'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/lazy_load_hooks.rb:36:in `execute_hook'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/lazy_load_hooks.rb:43:in `block in run_load_hooks'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/lazy_load_hooks.rb:42:in `each'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/lazy_load_hooks.rb:42:in `run_load_hooks'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/actionmailer-3.2.13/lib/action_mailer/base.rb:746:in `<class:Base>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/actionmailer-3.2.13/lib/action_mailer/base.rb:326:in `<module:ActionMailer>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/actionmailer-3.2.13/lib/action_mailer/base.rb:11:in `<top (required)>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/inflector/methods.rb:230:in `const_get'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/inflector/methods.rb:230:in `block in constantize'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/inflector/methods.rb:229:in `each'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/inflector/methods.rb:229:in `constantize'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/core_ext/string/inflections.rb:54:in `constantize'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/devise-3.0.0/app/mailers/devise/mailer.rb:1:in `<top (required)>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `block in require'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:236:in `load_dependency'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:359:in `require_or_load'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:313:in `depend_on'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:225:in `require_dependency'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/engine.rb:439:in `block (2 levels) in eager_load!'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/engine.rb:438:in `each'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/engine.rb:438:in `block in eager_load!'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/engine.rb:436:in `each'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/engine.rb:436:in `eager_load!'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/application/railties.rb:8:in `each'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/application/railties.rb:8:in `all'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/engine.rb:434:in `eager_load!'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/application/finisher.rb:53:in `block in <module:Finisher>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/initializable.rb:30:in `instance_exec'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/initializable.rb:30:in `run'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/initializable.rb:55:in `block in run_initializers'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/initializable.rb:54:in `each'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/initializable.rb:54:in `run_initializers'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/application.rb:136:in `initialize!'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/railtie/configurable.rb:30:in `method_missing'
from /Users/Rafael/Dev/Nuveo/StoresEngine/config/environment.rb:5:in `<top (required)>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `block in require'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:236:in `load_dependency'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/activesupport-3.2.13/lib/active_support/dependencies.rb:251:in `require'
from /Users/Rafael/Dev/Nuveo/StoresEngine/config.ru:3:in `block in <main>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/rack-1.4.5/lib/rack/builder.rb:51:in `instance_eval'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/rack-1.4.5/lib/rack/builder.rb:51:in `initialize'
from /Users/Rafael/Dev/Nuveo/StoresEngine/config.ru:in `new'
from /Users/Rafael/Dev/Nuveo/StoresEngine/config.ru:in `<main>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/rack-1.4.5/lib/rack/builder.rb:40:in `eval'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/rack-1.4.5/lib/rack/builder.rb:40:in `parse_file'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/rack-1.4.5/lib/rack/server.rb:200:in `app'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/commands/server.rb:46:in `app'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/rack-1.4.5/lib/rack/server.rb:304:in `wrapped_app'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/rack-1.4.5/lib/rack/server.rb:254:in `start'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/commands/server.rb:70:in `start'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/commands.rb:55:in `block in <top (required)>'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/commands.rb:50:in `tap'
from /Users/Rafael/.rvm/gems/ruby-1.9.3-p429/gems/railties-3.2.13/lib/rails/commands.rb:50:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'
但是，如果我禁用 config.cache_classes 将其设置为 false，则该错误将不再出现。但是我没有办法让 cache_classes = false 投入生产。
有人可以帮我弄这个吗？
非常感谢