Tracks permits deletion of a context in which action(s) exist.

Then on the home page I receive the following exception:

NoMethodError in Todo#list

You have a nil object when you didn't expect it!
The error occured while evaluating nil.hide?

RAILS_ROOT: .
Application Trace | Framework Trace | Full Trace

#{RAILS_ROOT}/app/controllers/todo_controller.rb:36:in `list'
#{RAILS_ROOT}/app/controllers/todo_controller.rb:36:in `list'

#{RAILS_ROOT}/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:75:in `method_missing'
#{RAILS_ROOT}/vendor/rails/activerecord/lib/active_record/associations/has_many_association.rb:90:in `method_missing'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/base.rb:853:in `perform_action_without_filters'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/filters.rb:332:in `perform_action_without_benchmark'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/benchmarking.rb:69:in `perform_action_without_rescue'
/usr/lib/ruby/1.8/benchmark.rb:293:in `measure'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/benchmarking.rb:69:in `perform_action_without_rescue'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/rescue.rb:82:in `perform_action'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/base.rb:369:in `process_without_session_management_support'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/session_management.rb:116:in `process'
#{RAILS_ROOT}/vendor/rails/railties/lib/dispatcher.rb:38:in `dispatch'
#{RAILS_ROOT}/vendor/rails/railties/lib/webrick_server.rb:117:in `handle_dispatch'
#{RAILS_ROOT}/vendor/rails/railties/lib/webrick_server.rb:83:in `service'
/usr/lib/ruby/1.8/webrick/httpserver.rb:104:in `service'
/usr/lib/ruby/1.8/webrick/httpserver.rb:65:in `run'
/usr/lib/ruby/1.8/webrick/server.rb:173:in `start_thread'
/usr/lib/ruby/1.8/webrick/server.rb:162:in `start_thread'
/usr/lib/ruby/1.8/webrick/server.rb:95:in `start'
/usr/lib/ruby/1.8/webrick/server.rb:92:in `start'
/usr/lib/ruby/1.8/webrick/server.rb:23:in `start'
/usr/lib/ruby/1.8/webrick/server.rb:82:in `start'
#{RAILS_ROOT}/vendor/rails/railties/lib/webrick_server.rb:69:in `dispatch'
#{RAILS_ROOT}/vendor/rails/railties/lib/commands/servers/webrick.rb:59
#{RAILS_ROOT}/vendor/rails/activesupport/lib/active_support/dependencies.rb:214:in `require'
#{RAILS_ROOT}/vendor/rails/railties/lib/commands/server.rb:28
script/server:3

#{RAILS_ROOT}/app/controllers/todo_controller.rb:36:in `list'
#{RAILS_ROOT}/vendor/rails/activerecord/lib/active_record/associations/association_proxy.rb:75:in `method_missing'
#{RAILS_ROOT}/vendor/rails/activerecord/lib/active_record/associations/has_many_association.rb:90:in `method_missing'
#{RAILS_ROOT}/app/controllers/todo_controller.rb:36:in `list'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/base.rb:853:in `perform_action_without_filters'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/filters.rb:332:in `perform_action_without_benchmark'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/benchmarking.rb:69:in `perform_action_without_rescue'
/usr/lib/ruby/1.8/benchmark.rb:293:in `measure'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/benchmarking.rb:69:in `perform_action_without_rescue'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/rescue.rb:82:in `perform_action'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/base.rb:369:in `process_without_session_management_support'
#{RAILS_ROOT}/vendor/rails/actionpack/lib/action_controller/session_management.rb:116:in `process'
#{RAILS_ROOT}/vendor/rails/railties/lib/dispatcher.rb:38:in `dispatch'
#{RAILS_ROOT}/vendor/rails/railties/lib/webrick_server.rb:117:in `handle_dispatch'
#{RAILS_ROOT}/vendor/rails/railties/lib/webrick_server.rb:83:in `service'
/usr/lib/ruby/1.8/webrick/httpserver.rb:104:in `service'
/usr/lib/ruby/1.8/webrick/httpserver.rb:65:in `run'
/usr/lib/ruby/1.8/webrick/server.rb:173:in `start_thread'
/usr/lib/ruby/1.8/webrick/server.rb:162:in `start_thread'
/usr/lib/ruby/1.8/webrick/server.rb:95:in `start'
/usr/lib/ruby/1.8/webrick/server.rb:92:in `start'
/usr/lib/ruby/1.8/webrick/server.rb:23:in `start'
/usr/lib/ruby/1.8/webrick/server.rb:82:in `start'
#{RAILS_ROOT}/vendor/rails/railties/lib/webrick_server.rb:69:in `dispatch'
#{RAILS_ROOT}/vendor/rails/railties/lib/commands/servers/webrick.rb:59
#{RAILS_ROOT}/vendor/rails/activesupport/lib/active_support/dependencies.rb:214:in `require'
#{RAILS_ROOT}/vendor/rails/railties/lib/commands/server.rb:28
script/server:3