带有设计的 Mongoid 似乎为我抛出了这个错误，无论何时使用设计。
undefined method `-' for nil:NilClass
这是堆栈跟踪
moped (1.2.7) lib/moped/cluster.rb:172:in `block in refresh'
moped (1.2.7) lib/moped/cluster.rb:179:in `each'
moped (1.2.7) lib/moped/cluster.rb:179:in `refresh'
moped (1.2.7) lib/moped/cluster.rb:132:in `nodes'
moped (1.2.7) lib/moped/cluster.rb:240:in `with_secondary'
moped (1.2.7) lib/moped/session/context.rb:104:in `with_node'
moped (1.2.7) lib/moped/session/context.rb:43:in `query'
moped (1.2.7) lib/moped/query.rb:112:in `first'
mongoid (3.0.10) lib/mongoid/contextual/mongo.rb:201:in `first'
mongoid (3.0.10) lib/mongoid/contextual.rb:18:in `first'
orm_adapter (0.4.0) lib/orm_adapter/adapters/mongoid.rb:22:in `get'
devise (2.1.2) lib/devise/models/authenticatable.rb:183:in `serialize_from_session'
devise (2.1.2) lib/devise/rails/warden_compat.rb:29:in `deserialize'
warden (1.2.1) lib/warden/session_serializer.rb:35:in `fetch'
warden (1.2.1) lib/warden/proxy.rb:212:in `user'
warden (1.2.1) lib/warden/proxy.rb:318:in `_perform_authentication'
warden (1.2.1) lib/warden/proxy.rb:127:in `authenticate!'
devise (2.1.2) lib/devise/controllers/helpers.rb:48:in `authenticate_user!'
activesupport (3.2.8) lib/active_support/callbacks.rb:418:in `_run__532752988157179990__process_action__39271927218028622__callbacks'
activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.8) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
activesupport (3.2.8) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.8) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (3.2.8) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (3.2.8) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
activesupport (3.2.8) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.8) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.8) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.8) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
actionpack (3.2.8) lib/action_controller/metal/params_wrapper.rb:207:in `process_action'
actionpack (3.2.8) lib/abstract_controller/base.rb:121:in `process'
actionpack (3.2.8) lib/abstract_controller/rendering.rb:45:in `process'
actionpack (3.2.8) lib/action_controller/metal.rb:203:in `dispatch'
actionpack (3.2.8) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
actionpack (3.2.8) lib/action_controller/metal.rb:246:in `block in action'
actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:73:in `call'
actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:73:in `dispatch'
actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:36:in `call'
journey (1.0.4) lib/journey/router.rb:68:in `block in call'
journey (1.0.4) lib/journey/router.rb:56:in `each'
journey (1.0.4) lib/journey/router.rb:56:in `call'
actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:600:in `call'
mongoid (3.0.10) lib/rack/mongoid/middleware/identity_map.rb:34:in `call'
warden (1.2.1) lib/warden/manager.rb:35:in `block in call'
warden (1.2.1) lib/warden/manager.rb:34:in `catch'
warden (1.2.1) lib/warden/manager.rb:34:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
rack (1.4.1) lib/rack/etag.rb:23:in `call'
rack (1.4.1) lib/rack/conditionalget.rb:25:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/head.rb:14:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/flash.rb:242:in `call'
rack (1.4.1) lib/rack/session/abstract/id.rb:205:in `context'
rack (1.4.1) lib/rack/session/abstract/id.rb:200:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/cookies.rb:339:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `_run__4054107343433525264__call__3237741633973160553__callbacks'
activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.8) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
activesupport (3.2.8) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.8) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/reloader.rb:65:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
railties (3.2.8) lib/rails/rack/logger.rb:26:in `call_app'
railties (3.2.8) lib/rails/rack/logger.rb:16:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/request_id.rb:22:in `call'
rack (1.4.1) lib/rack/methodoverride.rb:21:in `call'
rack (1.4.1) lib/rack/runtime.rb:17:in `call'
activesupport (3.2.8) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.4.1) lib/rack/lock.rb:15:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/static.rb:62:in `call'
railties (3.2.8) lib/rails/engine.rb:479:in `call'
railties (3.2.8) lib/rails/application.rb:223:in `call'
rack (1.4.1) lib/rack/content_length.rb:14:in `call'
railties (3.2.8) lib/rails/rack/log_tailer.rb:17:in `call'
rack (1.4.1) lib/rack/handler/webrick.rb:59:in `service'
/Users/amit/.rvm/rubies/ruby-1.9.3-p286/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
/Users/amit/.rvm/rubies/ruby-1.9.3-p286/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
/Users/amit/.rvm/rubies/ruby-1.9.3-p286/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'
控制器有一个 before_filter :authenticate_user！对此发表评论，允许页面工作。
这里可能有什么问题？
我已经尝试通过这样做来破坏所有设计安装
rails d devise user
rails d devise:views
rails d devise:install
然后重新安装设计，它没有帮助。有任何想法吗？