NoMethodError: undefined method `[]' for nil:NilClass

[doriath]

Check full details on Airbrake: #69952686

Backtrace:

```
[PROJECT_ROOT]/lib/online_judges/spoj/problem_page.rb:77:in last_page
[PROJECT_ROOT]/lib/online_judges/spoj/problem_page.rb:19:in problem
[PROJECT_ROOT]/lib/online_judges/english_spoj.rb:25:in fetch_problem
[PROJECT_ROOT]/app/models/problem.rb:31:in find_or_fetch_by
[PROJECT_ROOT]/app/models/online_judge.rb:56:in update_attempt
[PROJECT_ROOT]/app/models/online_judge.rb:17:in block in refresh
[PROJECT_ROOT]/app/models/online_judge.rb:17:in each
[PROJECT_ROOT]/app/models/online_judge.rb:17:in refresh
[PROJECT_ROOT]/app/controllers/online_judges_controller.rb:37:in refresh
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_controller/metal/implicit_render.rb:4:in send_action
[GEM_ROOT]/gems/actionpack-3.2.11/lib/abstract_controller/base.rb:167:in process_action
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_controller/metal/rendering.rb:10:in process_action
[GEM_ROOT]/gems/actionpack-3.2.11/lib/abstract_controller/callbacks.rb:18:in block in process_action
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:436:in _run__221995238__process_action__741546866__callbacks
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:405:in __run_callback
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:385:in _run_process_action_callbacks
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:81:in run_callbacks
[GEM_ROOT]/gems/actionpack-3.2.11/lib/abstract_controller/callbacks.rb:17:in process_action
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_controller/metal/rescue.rb:29:in process_action
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_controller/metal/instrumentation.rb:30:in block in process_action
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/notifications.rb:123:in block in instrument
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/notifications/instrumenter.rb:20:in instrument
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/notifications.rb:123:in instrument
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_controller/metal/instrumentation.rb:29:in process_action
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_controller/metal/params_wrapper.rb:207:in process_action
[GEM_ROOT]/gems/newrelic_rpm-3.5.0.1/lib/new_relic/agent/instrumentation/rails3/action_controller.rb:34:in block in process_action
[GEM_ROOT]/gems/newrelic_rpm-3.5.0.1/lib/new_relic/agent/instrumentation/controller_instrumentation.rb:268:in block in perform_action_with_newrelic_trace
[GEM_ROOT]/gems/newrelic_rpm-3.5.0.1/lib/new_relic/agent/method_tracer.rb:242:in trace_execution_scoped
[GEM_ROOT]/gems/newrelic_rpm-3.5.0.1/lib/new_relic/agent/instrumentation/controller_instrumentation.rb:263:in perform_action_with_newrelic_trace
[GEM_ROOT]/gems/newrelic_rpm-3.5.0.1/lib/new_relic/agent/instrumentation/rails3/action_controller.rb:33:in process_action
[GEM_ROOT]/gems/actionpack-3.2.11/lib/abstract_controller/base.rb:121:in process
[GEM_ROOT]/gems/actionpack-3.2.11/lib/abstract_controller/rendering.rb:45:in process
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_controller/metal.rb:203:in dispatch
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_controller/metal/rack_delegation.rb:14:in dispatch
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_controller/metal.rb:246:in block in action
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:73:in call
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:73:in dispatch
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:36:in call
[GEM_ROOT]/gems/journey-1.0.4/lib/journey/router.rb:68:in block in call
[GEM_ROOT]/gems/journey-1.0.4/lib/journey/router.rb:56:in each
[GEM_ROOT]/gems/journey-1.0.4/lib/journey/router.rb:56:in call
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/routing/route_set.rb:601:in call
[GEM_ROOT]/gems/newrelic_rpm-3.5.0.1/lib/new_relic/rack/error_collector.rb:8:in call
[GEM_ROOT]/gems/newrelic_rpm-3.5.0.1/lib/new_relic/rack/browser_monitoring.rb:12:in call
[GEM_ROOT]/gems/mongoid-3.0.10/lib/rack/mongoid/middleware/identity_map.rb:34:in call
[GEM_ROOT]/gems/warden-1.2.1/lib/warden/manager.rb:35:in block in call
[GEM_ROOT]/gems/warden-1.2.1/lib/warden/manager.rb:34:in catch
[GEM_ROOT]/gems/warden-1.2.1/lib/warden/manager.rb:34:in call
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/middleware/best_standards_support.rb:17:in call
[GEM_ROOT]/gems/rack-1.4.3/lib/rack/etag.rb:23:in call
[GEM_ROOT]/gems/rack-1.4.3/lib/rack/conditionalget.rb:35:in call
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/middleware/head.rb:14:in call
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/middleware/params_parser.rb:21:in call
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/middleware/flash.rb:242:in call
[GEM_ROOT]/gems/rack-1.4.3/lib/rack/session/abstract/id.rb:210:in context
[GEM_ROOT]/gems/rack-1.4.3/lib/rack/session/abstract/id.rb:205:in call
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/middleware/cookies.rb:341:in call
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/middleware/callbacks.rb:28:in block in call
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:405:in _run__402358253__call__651117410__callbacks
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:405:in __run_callback
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:385:in _run_call_callbacks
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/callbacks.rb:81:in run_callbacks
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/middleware/callbacks.rb:27:in call
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/middleware/remote_ip.rb:31:in call
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/middleware/debug_exceptions.rb:16:in call
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/middleware/show_exceptions.rb:56:in call
[GEM_ROOT]/gems/railties-3.2.11/lib/rails/rack/logger.rb:32:in call_app
[GEM_ROOT]/gems/railties-3.2.11/lib/rails/rack/logger.rb:16:in block in call
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/tagged_logging.rb:22:in tagged
[GEM_ROOT]/gems/railties-3.2.11/lib/rails/rack/logger.rb:16:in call
[GEM_ROOT]/gems/actionpack-3.2.11/lib/action_dispatch/middleware/request_id.rb:22:in call
[GEM_ROOT]/gems/rack-1.4.3/lib/rack/methodoverride.rb:21:in call
[GEM_ROOT]/gems/rack-1.4.3/lib/rack/runtime.rb:17:in call
[GEM_ROOT]/gems/activesupport-3.2.11/lib/active_support/cache/strategy/local_cache.rb:72:in call
[GEM_ROOT]/gems/rack-1.4.3/lib/rack/lock.rb:15:in call
[GEM_ROOT]/gems/rack-cache-1.2/lib/rack/cache/context.rb:136:in forward
[GEM_ROOT]/gems/rack-cache-1.2/lib/rack/cache/context.rb:143:in pass
[GEM_ROOT]/gems/rack-cache-1.2/lib/rack/cache/context.rb:155:in invalidate
[GEM_ROOT]/gems/rack-cache-1.2/lib/rack/cache/context.rb:71:in call!
[GEM_ROOT]/gems/rack-cache-1.2/lib/rack/cache/context.rb:51:in call
[GEM_ROOT]/gems/railties-3.2.11/lib/rails/engine.rb:479:in call
[GEM_ROOT]/gems/railties-3.2.11/lib/rails/application.rb:223:in call
[GEM_ROOT]/gems/railties-3.2.11/lib/rails/railtie/configurable.rb:30:in method_missing
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/rack/request_handler.rb:96:in process_request
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/abstract_request_handler.rb:516:in accept_and_process_next_request
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/abstract_request_handler.rb:274:in main_loop
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/rack/application_spawner.rb:206:in start_request_handler
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/rack/application_spawner.rb:171:in block in handle_spawn_application
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/utils.rb:470:in safe_fork
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/rack/application_spawner.rb:166:in handle_spawn_application
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/abstract_server.rb:357:in server_main_loop
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/abstract_server.rb:206:in start_synchronously
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/abstract_server.rb:180:in start
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/rack/application_spawner.rb:129:in start
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/spawn_manager.rb:253:in block (2 levels) in spawn_rack_application
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/abstract_server_collection.rb:132:in lookup_or_add
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/spawn_manager.rb:246:in block in spawn_rack_application
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/abstract_server_collection.rb:82:in block in synchronize
:0:in 
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/abstract_server_collection.rb:79:in synchronize
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/spawn_manager.rb:244:in spawn_rack_application
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/spawn_manager.rb:137:in spawn_application
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/spawn_manager.rb:275:in handle_spawn_application
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/abstract_server.rb:357:in server_main_loop
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/lib/phusion_passenger/abstract_server.rb:206:in start_synchronously
/usr/lib/ruby/gems/1.9.1/gems/passenger-3.0.18/helper-scripts/passenger-spawn-server:99:in <main>
```