Redmine

I've created a new wiki page. I haven't saved it yet. When I click on "preview" Redmine produces an internal server error. I'm using HEAD. Here is the relevant log output:

Processing WikiController#preview (for 156.148.120.93 at 2008-05-23 11:59:02) [POST]
  Session ID: 76182564b0927e5bbf6ecf86fb74f26b
  Parameters: {"commit"=>"Save", "action"=>"preview", "id"=>"pgds", "controller"=>"wiki",
 "content"=>{"comments"=>"", "text"=>"h1. Modelling genealogy", "version"=>"0"}, 
 "page"=>"Modelling_genealogy"}

NoMethodError (undefined method `editable_by?' for nil:NilClass):
    /app/controllers/wiki_controller.rb:197:in `editable?'
    /app/controllers/wiki_controller.rb:165:in `preview'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/base.rb:1158:in `send'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/base.rb:1158:in `perform_action_without_filters'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/filters.rb:697:in `call_filters'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/filters.rb:689:in `perform_action_without_benchmark'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'
    /usr/lib/ruby/1.8/benchmark.rb:293:in `measure'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/rescue.rb:199:in `perform_action_without_caching'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/caching.rb:678:in `perform_action'
    /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/active_record/connection_adapters/abstract/query_cache.rb:33:in `cache'
    /usr/lib/ruby/gems/1.8/gems/activerecord-2.0.2/lib/active_record/query_cache.rb:8:in `cache'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/caching.rb:677:in `perform_action'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/base.rb:524:in `send'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/base.rb:524:in `process_without_filters'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/filters.rb:685:in `process_without_session_management_support'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/session_management.rb:123:in `process'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/base.rb:388:in `process'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/dispatcher.rb:171:in `handle_request'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/dispatcher.rb:115:in `dispatch'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/dispatcher.rb:126:in `dispatch_cgi'
    /usr/lib/ruby/gems/1.8/gems/actionpack-2.0.2/lib/action_controller/dispatcher.rb:9:in `dispatch'
    /usr/lib/ruby/gems/1.8/gems/rails-2.0.2/lib/fcgi_handler.rb:101:in `process_request'
    /usr/lib/ruby/gems/1.8/gems/rails-2.0.2/lib/fcgi_handler.rb:149:in `with_signal_handler'
    /usr/lib/ruby/gems/1.8/gems/rails-2.0.2/lib/fcgi_handler.rb:99:in `process_request'
    /usr/lib/ruby/gems/1.8/gems/rails-2.0.2/lib/fcgi_handler.rb:77:in `process_each_request'
    /usr/lib/ruby/gems/1.8/gems/fcgi-0.8.7/lib/fcgi.rb:612:in `each_cgi'
    /usr/lib/ruby/gems/1.8/gems/fcgi-0.8.7/lib/fcgi.rb:609:in `each'
    /usr/lib/ruby/gems/1.8/gems/fcgi-0.8.7/lib/fcgi.rb:609:in `each_cgi'
    /usr/lib/ruby/gems/1.8/gems/rails-2.0.2/lib/fcgi_handler.rb:76:in `process_each_request'
    /usr/lib/ruby/gems/1.8/gems/rails-2.0.2/lib/fcgi_handler.rb:50:in `process!'
    /usr/lib/ruby/gems/1.8/gems/rails-2.0.2/lib/fcgi_handler.rb:24:in `process!'
    /public/dispatch.fcgi:24

Rendering /var/www/redmine/public/500.html (500 Internal Server Error)