当我尝试运行我的 rails 服务器时，我收到以下错误（重要提示：我刚刚将我的代码从 Github 拉到 Nitrous.Io，并开始在应用程序上工作）：
/home/action/.rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.0/lib/active_support/inflector/methods.rb:226:in `const_get': uninitialized constant User (NameEr
ror) from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.0/lib/active_support/inflector/methods.rb:226:in `block in constantize'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.0/lib/active_support/inflector/methods.rb:224:in `each'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.0/lib/active_support/inflector/methods.rb:224:in `inject'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.0/lib/active_support/inflector/methods.rb:224:in `constantize'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise.rb:285:in `get'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise/mapping.rb:77:in `to'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise/mapping.rb:72:in `modules'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise/mapping.rb:89:in `routes'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise/mapping.rb:156:in `default_used_route'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise/mapping.rb:66:in `initialize'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise.rb:319:in `new'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise.rb:319:in `add_mapping'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise/rails/routes.rb:210:in `block in devise_for'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise/rails/routes.rb:209:in `each'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/devise-3.1.1/lib/devise/rails/routes.rb:209:in `devise_for'
from /home/action/pinteresting/config/routes.rb:4:in `block in <top (required)>'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/actionpack-4.0.0/lib/action_dispatch/routing/route_set.rb:316:in `instance_exec'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/actionpack-4.0.0/lib/action_dispatch/routing/route_set.rb:316:in `eval_block'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/actionpack-4.0.0/lib/action_dispatch/routing/route_set.rb:294:in `draw'
from /home/action/pinteresting/config/routes.rb:1:in `<top (required)>'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/application/routes_reloader.rb:40:in `block in load_paths'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/application/routes_reloader.rb:40:in `each'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/application/routes_reloader.rb:40:in `load_paths'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/application/routes_reloader.rb:16:in `reload!'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/application/routes_reloader.rb:26:in `block in updater'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.0/lib/active_support/file_update_checker.rb:75:in `call'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/activesupport-4.0.0/lib/active_support/file_update_checker.rb:75:in `execute'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/application/routes_reloader.rb:27:in `updater'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/application/routes_reloader.rb:6:in `execute_if_updated'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/application/finisher.rb:69:in `block in <module:Finisher>'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/initializable.rb:30:in `instance_exec'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/initializable.rb:30:in `run'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/initializable.rb:55:in `block in run_initializers'
from /home/action/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:150:in `block in tsort_each'
from /home/action/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:183:in `block (2 levels) in each_strongly_connected_component'
from /home/action/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:219:in `each_strongly_connected_component_from'
from /home/action/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:182:in `block in each_strongly_connected_component'
from /home/action/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:180:in `each'
from /home/action/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:180:in `each_strongly_connected_component'
from /home/action/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/tsort.rb:148:in `tsort_each'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/initializable.rb:54:in `run_initializers'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/application.rb:215:in `initialize!'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/railtie/configurable.rb:30:in `method_missing'
from /home/action/pinteresting/config/environment.rb:5:in `<top (required)>'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/application.rb:189:in `require_environment!'
from /home/action/.rvm/gems/ruby-2.0.0-p247/gems/railties-4.0.0/lib/rails/commands.rb:45:in `<top (required)>'
from bin/rails:4:in `require'
from bin/rails:4:in `<main>'