我正在尝试在本地运行我的Rails应用程序，以便它将指向Heroku上已部署应用程序使用的数据库。使用heroku pg:credentials DATABASE，我能够获取有关生产数据库的信息，并使用它来填充database.yml中的生产信息。但是，当我运行rails s -e production时，我收到以下错误：
=> Booting Puma
=> Rails 4.2.6 application starting in production on http://localhost:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Exiting
/Users/Robert/.rvm/gems/ruby-2.2.2/gems/braintree-2.68.2/lib/braintree/configuration.rb:59:in `environment=': undefined method `to_sym' for nil:NilClass (NoMethodError)
from /Users/Robert/Developer/Git-Repositories/inspectx-live/config/initializers/braintree.rb:1:in `<top (required)>'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:268:in `load'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:268:in `block in load'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:240:in `load_dependency'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:268:in `load'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/engine.rb:652:in `block in load_config_initializer'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/activesupport-4.2.6/lib/active_support/notifications.rb:166:in `instrument'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/engine.rb:651:in `load_config_initializer'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/engine.rb:616:in `block (2 levels) in <class:Engine>'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/engine.rb:615:in `each'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/engine.rb:615:in `block in <class:Engine>'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/initializable.rb:30:in `instance_exec'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/initializable.rb:30:in `run'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/initializable.rb:55:in `block in run_initializers'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:226:in `block in tsort_each'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:348:in `block (2 levels) in each_strongly_connected_component'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:420:in `block (2 levels) in each_strongly_connected_component_from'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:429:in `each_strongly_connected_component_from'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:419:in `block in each_strongly_connected_component_from'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/initializable.rb:44:in `each'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/initializable.rb:44:in `tsort_each_child'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:413:in `call'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:413:in `each_strongly_connected_component_from'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:347:in `block in each_strongly_connected_component'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:345:in `each'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:345:in `call'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:345:in `each_strongly_connected_component'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:224:in `tsort_each'
from /Users/Robert/.rvm/rubies/ruby-2.2.2/lib/ruby/2.2.0/tsort.rb:203:in `tsort_each'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/initializable.rb:54:in `run_initializers'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/application.rb:352:in `initialize!'
from /Users/Robert/Developer/Git-Repositories/inspectx-live/config/environment.rb:5:in `<top (required)>'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `require'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `block in require'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:240:in `load_dependency'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/activesupport-4.2.6/lib/active_support/dependencies.rb:274:in `require'
from /Users/Robert/Developer/Git-Repositories/inspectx-live/config.ru:3:in `block in <main>'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/rack-1.6.4/lib/rack/builder.rb:55:in `instance_eval'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/rack-1.6.4/lib/rack/builder.rb:55:in `initialize'
from /Users/Robert/Developer/Git-Repositories/inspectx-live/config.ru:in `new'
from /Users/Robert/Developer/Git-Repositories/inspectx-live/config.ru:in `<main>'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/rack-1.6.4/lib/rack/builder.rb:49:in `eval'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/rack-1.6.4/lib/rack/builder.rb:49:in `new_from_string'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/rack-1.6.4/lib/rack/builder.rb:40:in `parse_file'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/rack-1.6.4/lib/rack/server.rb:299:in `build_app_and_options_from_config'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/rack-1.6.4/lib/rack/server.rb:208:in `app'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/commands/server.rb:61:in `app'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/rack-1.6.4/lib/rack/server.rb:336:in `wrapped_app'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/rack-1.6.4/lib/rack/server.rb:272:in `start'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/commands/server.rb:80:in `start'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:80:in `block in server'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:75:in `tap'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:75:in `server'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/railties-4.2.6/lib/rails/commands.rb:17:in `<top (required)>'
from /Users/Robert/Developer/Git-Repositories/inspectx-live/bin/rails:9:in `require'
from /Users/Robert/Developer/Git-Repositories/inspectx-live/bin/rails:9:in `<top (required)>'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/spring-1.7.1/lib/spring/client/rails.rb:28:in `load'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/spring-1.7.1/lib/spring/client/rails.rb:28:in `call'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/spring-1.7.1/lib/spring/client/command.rb:7:in `call'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/spring-1.7.1/lib/spring/client.rb:30:in `run'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/spring-1.7.1/bin/spring:49:in `<top (required)>'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/spring-1.7.1/lib/spring/binstub.rb:11:in `load'
from /Users/Robert/.rvm/gems/ruby-2.2.2/gems/spring-1.7.1/lib/spring/binstub.rb:11:in `<top (required)>'
from /Users/Robert/Developer/Git-Repositories/inspectx-live/bin/spring:13:in `require'
from /Users/Robert/Developer/Git-Repositories/inspectx-live/bin/spring:13:in `<top (required)>'
from bin/rails:3:in `load'
from bin/rails:3:in `<main>'
我对Rails比较新，所以我不知道该怎么办。我认为这与Braintree集成有关，但我真的不确定。
编辑：以下是config / initializers / braintree.rb的内容：
Braintree::Configuration.environment = ENV['BRAINTREE_ENV']
Braintree::Configuration.merchant_id = ENV['BRAINTREE_MERCHANT_ID']
Braintree::Configuration.public_key = ENV['BRAINTREE_PUBLIC_KEY']
Braintree::Configuration.private_key = ENV['BRAINTREE_PRIVATE_KEY']
关于braintree.rb的说明：没有隐私的隐私信息。以上就是它在braintree.rb中的显示方式。我最初没有设置Braintree集成，所以我不确定ENV字段中是否应该有私人信息。