Ruby on rails 在Rails 5.1.0上生成模型时出现意外错误

我不熟悉rails平台。我正在使用公寓gem构建一个多租户应用程序。我按照这个指南学习如何使用这个宝石。但当我搭建或生成用户模型时，我得到了以下错误：

$rails g scaffold用户电子邮件名称子域
C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/actionpack-5.1.0/lib/action\u dispatch/middleware/stack.rb:35:in`build'：用于“Apartme nt:：电梯：：子域”的未定义方法`new'：字符串（NoMethodError）
你是说？下一个
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/actionpack-5.1.0/lib/action\u dispatch/middleware/stack.rb:99:in'block in build'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/actionpack-5.1.0/lib/action\u dispatch/middleware/stack.rb:99:in'each'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/actionpack-5.1.0/lib/action\u dispatch/middleware/stack.rb:99:in'inject'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/actionpack-5.1.0/lib/action\u dispatch/middleware/stack.rb:99:in'build'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/engine.rb:508:in'block in app'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/engine.rb:504:在“同步”中
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/engine.rb:504:in'app'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/application/finisher.rb:45:in'block in'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/initializable.rb:30:in'instance_exec'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/initializable.rb:30:in'run'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/initializable.rb:59:“运行中的块\初始化器”
from C:/RailsInstaller/Ruby2.3.0/lib/ruby/2.3.0/tsort.rb:228:in'block i n tsort_each'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/2.3.0/tsort.rb:350:in `每个强连接的\u组件中的块（2个级别）'
from C:/RailsInstaller/Ruby2.3.0/lib/ruby/2.3.0/tsort.rb:431:in“每个连接的组件”
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/2.3.0/tsort.rb:349:“每个强连接的组件中的块”
from C:/RailsInstaller/Ruby2.3.0/lib/ruby/2.3.0/tsort.rb:347:in'each'
from C:/RailsInstaller/Ruby2.3.0/lib/ruby/2.3.0/tsort.rb:347:in'call'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/2.3.0/tsort.rb:347:“每个紧密连接的组件”
from C:/RailsInstaller/Ruby2.3.0/lib/ruby/2.3.0/tsort.rb:226:in'tsort_e ach'
from C:/RailsInstaller/Ruby2.3.0/lib/ruby/2.3.0/tsort.rb:205:in'tsort_e ach'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/initializable.rb:58:in'run_initializers'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/application.rb:353:in'initialize！'
来自C:/Sites/multi-tenant\u app/config/environment.rb:5:in`'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/application.rb:329:in'require'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/application.rb:329:in'require_environment！'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/command/actions.rb:16:“需要应用程序和环境！”
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/railties-5.1.0/lib/rails/commands/generate/generate_command.rb:19:in'perform'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/thor-0.19.4/li b/thor/command.rb:27:in'run'
来自C:/RailsInstaller/Ruby2.3.0/lib/ruby/gems/2.3.0/gems/thor-0.19.4/li b/thor/invocation.rb:126:in'invoke_command'
require 'apartment/elevators/subdomain'

config.middleware.use Apartment::Elevators::Subdomain