ruby-on-rails - Rails 3 の連絡先フォームにメソッド エラーはありません

Question

次のチュートリアルを使用して連絡先フォームをまとめています: http://matharvard.ca/posts/2011/aug/22/contact-form-in-rails-3/

すべての指示に従いましたが、アプリの連絡先ページにアクセスしようとすると、何らかの理由でこのエラーが発生し続けます。

NoMethodError in Contact#new

undefined method `[]' for nil:NilClass
Extracted source (around line #1):

1: <%= form_for @message, :url => contact_path do |form| %>
2:   <fieldset class="fields">
3:     <div class="field">
4:       <%= form.label :name %>

ここで何が欠けていますか？

new.html.erb

<%= form_for @message, :url => contact_path do |form| %>
<fieldset class="fields">
<div class="field">
  <%= form.label :name %>
  <%= form.text_field :name %>
</div>

<div class="field">
  <%= form.label :email %>
  <%= form.text_field :email %>
</div>
<div class="field">
  <%= form.label :subject %>
  <%= form.text_field :subject %>
</div>

<div class="field">
  <%= form.label :body %>
  <%= form.text_area :body %>
</div>
</fieldset>

<fieldset class="actions">
<%= form.submit "Send" %>
</fieldset>
<% end %>

contact_controller.rb

class ContactController < ApplicationController

def new
  @message = Message.new
end

def create
  @message = Message.new(params[:message])

if @message.valid?
  NotificationsMailer.new_message(@message).deliver
  redirect_to(root_path, :notice => "Message was successfully sent.")
else
  flash.now.alert = "Please fill all fields."
  render :new
end
end
end

notifications_mailer.rb

class NotificationsMailer < ActionMailer::Base

default :from => "myemail@gmail.com"
default :to => "myemail@gmail.com"

def new_message(message)
  @message = message
  mail(:subject => "[myemail@gmail.com] #{message.subject}")
end
end