Strange error message when rendering the scaffold form

Hello everyone, I am developing my application and I created a
scaffold called listas, but when I acess /listas/new I get this error

NoMethodError in Listas#new

Showing /home/rodrigo3n/code/listeiroo/app/views/listas/_form.html.erb
where line #15 raised:

undefined method `deep_symbolize_keys' for nil:NilClass
Extracted source (around line #15):

12: <% end %>
14: <div class="field">
15: <%= f.label :nome %><br />
16: <%= f.text_field :nome %>
17: </div>
18: <div class="field">
Trace of template inclusion: app/views/listas/new.html.erb

I am using Rails 3RC and Ruby 1.9.2-rc2. This error is very strange to
me because I did just create the scaffold via "% rails g scaffold" and
then this error appeared. Do you know why?

Rodrigo Alves Vieira

Did you migrate the database?