Topic: shows/new failing

First the shows/new failing, I get with no shows in database:

undefined method `model_name' for NilClass:Class

Extracted source (around line #1):

1: <%= form_for(@show) do |f| %>
2:   <% if @show.errors.any? %>
3:     <div id="error_explanation">
4:       <h2><%= pluralize(@show.errors.count, "error") %> prohibited this show from being saved:</h2>

The active_scaffold controller looks like:

class ShowsController < ApplicationController
  active_scaffold :show do |conf|
    conf.columns = [ :name, :title, :director,
                     :production_date, :delivery_date, :studio, :distributor ]
    conf.actions = [ :list, :create, :show, :update ]
  end
end