TypeError in NewscenterController#index

can't convert nil into String

RAILS_ROOT: /usr/web/ftweb

Application Trace | Framework Trace | Full Trace
/usr/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/core_ext/string/output_safety.rb:25:in `add_without_safety'
/usr/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/core_ext/string/output_safety.rb:25:in `+'
/usr/web/ftweb/app/models/category.rb:35:in `categroycompanyid'
/usr/web/ftweb/app/helpers/application_helper.rb:17:in `navigation_menu'
/usr/web/ftweb/app/controllers/newscenter_controller.rb:19:in `index'

Request

Parameters:

None

Show session dump

Response

headers:

{"Content-Type"=>"text/html;charset=utf-8",
 "Cache-Control"=>"no-cache"}