NoMethodError: undefined method `html_columns' for nil:NilClass

ERROR MESSAGE:
NoMethodError: undefined method `html_columns' for nil:NilClass

WHERE:
registrations#upload

app/views/registrations/index.html.erb:26
app/controllers/registrations_controller.rb:176

URL:
http://event.fkgent.be/events/4/registrations/upload

BROWSER:
100.0%	Safari 5.1.9 (OS X 10.6.8)

USER:
Id:	53


FULL BACKTRACE:
[GEM_ROOT]/gems/datagrid-1.0.5/app/views/datagrid/_head.html.erb:2
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/template.rb:143
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/notifications.rb:161
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/template.rb:141
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/partial_renderer.rb:306
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/partial_renderer.rb:279
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/abstract_renderer.rb:38
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/notifications.rb:159
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/notifications/instrumenter.rb:20
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/notifications.rb:159
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/abstract_renderer.rb:38
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/partial_renderer.rb:278
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/renderer.rb:47
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/renderer.rb:21
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/helpers/rendering_helper.rb:24
[GEM_ROOT]/gems/datagrid-1.0.5/lib/datagrid/renderer.rb:56
[GEM_ROOT]/gems/datagrid-1.0.5/lib/datagrid/helper.rb:39
app/views/registrations/index.html.erb:26
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/template.rb:143
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/notifications.rb:161
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/template.rb:141
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/template_renderer.rb:49
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/abstract_renderer.rb:38
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/notifications.rb:159
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/notifications/instrumenter.rb:20
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/notifications.rb:159
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/abstract_renderer.rb:38
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/template_renderer.rb:48
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/template_renderer.rb:56
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/template_renderer.rb:47
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/template_renderer.rb:17
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/renderer.rb:42
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_view/renderer/renderer.rb:23
[GEM_ROOT]/gems/actionpack-4.0.0/lib/abstract_controller/rendering.rb:127
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/streaming.rb:219
[GEM_ROOT]/gems/actionpack-4.0.0/lib/abstract_controller/rendering.rb:120
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/rendering.rb:33
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/renderers.rb:26
[GEM_ROOT]/gems/actionpack-4.0.0/lib/abstract_controller/rendering.rb:97
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/rendering.rb:16
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/instrumentation.rb:41
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/core_ext/benchmark.rb:12
/usr/local/rvm/rubies/ruby-2.1.0/lib/ruby/2.1.0/benchmark.rb:294
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/core_ext/benchmark.rb:12
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/instrumentation.rb:41
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/instrumentation.rb:84
[GEM_ROOT]/gems/activerecord-4.0.0/lib/active_record/railties/controller_runtime.rb:25
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/instrumentation.rb:40
app/controllers/registrations_controller.rb:176
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/implicit_render.rb:4
[GEM_ROOT]/gems/actionpack-4.0.0/lib/abstract_controller/base.rb:189
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/rendering.rb:10
[GEM_ROOT]/gems/actionpack-4.0.0/lib/abstract_controller/callbacks.rb:18
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/callbacks.rb:443
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/callbacks.rb:80
[GEM_ROOT]/gems/actionpack-4.0.0/lib/abstract_controller/callbacks.rb:17
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/rescue.rb:29
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/instrumentation.rb:31
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/notifications.rb:159
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/notifications/instrumenter.rb:20
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/notifications.rb:159
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/instrumentation.rb:30
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/params_wrapper.rb:245
[GEM_ROOT]/gems/activerecord-4.0.0/lib/active_record/railties/controller_runtime.rb:18
[GEM_ROOT]/gems/actionpack-4.0.0/lib/abstract_controller/base.rb:136
[GEM_ROOT]/gems/actionpack-4.0.0/lib/abstract_controller/rendering.rb:44
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal.rb:195
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal/rack_delegation.rb:13
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_controller/metal.rb:231
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/routing/route_set.rb:80
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/routing/route_set.rb:80
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/routing/route_set.rb:48
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/journey/router.rb:71
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/journey/router.rb:59
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/journey/router.rb:59
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/routing/route_set.rb:655
[GEM_ROOT]/gems/devise_cas_authenticatable-1.3.2/lib/devise_cas_authenticatable/single_sign_out/rack.rb:11
[GEM_ROOT]/gems/warden-1.2.3/lib/warden/manager.rb:35
[GEM_ROOT]/gems/warden-1.2.3/lib/warden/manager.rb:34
[GEM_ROOT]/gems/warden-1.2.3/lib/warden/manager.rb:34
[GEM_ROOT]/gems/rack-1.5.2/lib/rack/etag.rb:23
[GEM_ROOT]/gems/rack-1.5.2/lib/rack/conditionalget.rb:35
[GEM_ROOT]/gems/rack-1.5.2/lib/rack/head.rb:11
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/middleware/params_parser.rb:27
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/middleware/flash.rb:241
[GEM_ROOT]/gems/rack-1.5.2/lib/rack/session/abstract/id.rb:225
[GEM_ROOT]/gems/rack-1.5.2/lib/rack/session/abstract/id.rb:220
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/middleware/cookies.rb:486
[GEM_ROOT]/gems/activerecord-4.0.0/lib/active_record/query_cache.rb:36
[GEM_ROOT]/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract/connection_pool.rb:626
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/middleware/callbacks.rb:29
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/callbacks.rb:373
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/callbacks.rb:80
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/middleware/callbacks.rb:27
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/middleware/remote_ip.rb:76
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/middleware/debug_exceptions.rb:17
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/middleware/show_exceptions.rb:30
[GEM_ROOT]/gems/railties-4.0.0/lib/rails/rack/logger.rb:38
[GEM_ROOT]/gems/railties-4.0.0/lib/rails/rack/logger.rb:21
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/tagged_logging.rb:67
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/tagged_logging.rb:25
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/tagged_logging.rb:67
[GEM_ROOT]/gems/railties-4.0.0/lib/rails/rack/logger.rb:21
[GEM_ROOT]/gems/actionpack-4.0.0/lib/action_dispatch/middleware/request_id.rb:21
[GEM_ROOT]/gems/rack-1.5.2/lib/rack/methodoverride.rb:21
[GEM_ROOT]/gems/rack-1.5.2/lib/rack/runtime.rb:17
[GEM_ROOT]/gems/activesupport-4.0.0/lib/active_support/cache/strategy/local_cache.rb:83
[GEM_ROOT]/gems/railties-4.0.0/lib/rails/engine.rb:511
[GEM_ROOT]/gems/railties-4.0.0/lib/rails/application.rb:97
[GEM_ROOT]/gems/puma-2.7.1/lib/puma/configuration.rb:68
[GEM_ROOT]/gems/puma-2.7.1/lib/puma/server.rb:486
[GEM_ROOT]/gems/puma-2.7.1/lib/puma/server.rb:357
[GEM_ROOT]/gems/puma-2.7.1/lib/puma/server.rb:250
[GEM_ROOT]/gems/puma-2.7.1/lib/puma/thread_pool.rb:92
[GEM_ROOT]/gems/puma-2.7.1/lib/puma/thread_pool.rb:92