key not found error

Any ideas what the problem is here? It's showing up on the edit page
for a restful resource.

Extracted source (around line #3):

1: <h1>Editing content</h1>
2:
3: <% form_for([:admin, @content]) do |f| %>
4: <%= f.error_messages %>
5:
6: <p>

Trace
/usr/local/lib/ruby/gems/1.8/gems/facets-2.4.1/lib/facets/hash/
slice.rb:8:in `fetch'
/usr/local/lib/ruby/gems/1.8/gems/facets-2.4.1/lib/facets/hash/
slice.rb:8:in `slice'
/usr/local/lib/ruby/gems/1.8/gems/facets-2.4.1/lib/facets/hash/
slice.rb:7:in `each'
/usr/local/lib/ruby/gems/1.8/gems/facets-2.4.1/lib/facets/hash/
slice.rb:7:in `slice'
/usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/
helpers/form_helper.rb:699:in `initialize'
/usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/
helpers/form_helper.rb:317:in `new'
/usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/
helpers/form_helper.rb:317:in `fields_for'
/usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_view/
helpers/form_helper.rb:253:in `form_for_without_haml'
/usr/local/lib/ruby/gems/1.8/gems/haml-2.0.0/lib/haml/helpers/
action_view_mods.rb:124:in `form_for'
app/views/admin/contents/edit.html.erb:3:in
`_run_erb_47app47views47admin47contents47edit46html46erb'

Install facets 2.4.0 and all should be good. Not sure what the error
is in 2.4.1 yet.

OK, it still happens with 2.4.0 too. Looks like facets has issues with
Rails 2.1