undefined method `model_name' for NilClass:Class and unable to find a linked object

I am using rails v-3.0.3 and ruby gem 1.8 and I am working on creating a new class called contact_info and link it to the person class. Here are the code excerpts from all the relevant files:

model/person.rb

 class Person < ActiveRecord::Base
has_one :contact_info, :dependent => :destroy
 attr_accessible :first_name, :last_name, :middle_initial, :email, :password, 
end

model/contact_info.rb

class ContactInfo < ActiveRecord::Base
  belongs_to :person
  attr_accessible :street_address_1, :street_address_2
end

controller/profile_chaperone_controller.rb

class ProfileChaperoneController < ApplicationController
  def add_info
@person = current_person
  end

views/profile_chaperone/add_info.html.erb

<% form_for @person.contact_info do |f| %>
      <%= f.submit %>
<% end %>

and here are the error messages when I go to the add_info page:

undefined method `model_name' for NilClass:Class

Extracted source (around line #44):

41: <!--Add contact info for Snapshot section of Profile--!>
42:   <div id="info">
43:     <br>
44: <% form_for @person.contact_info do |f| %>
45:   
46:       <%= f.submit %>
47: <% end %>

I have also tried to create a form for @person and it does work. So the problem seems to be establish the proper开发者_如何学Go linkage between person and contact_info. Here is the migration file:

class CreateContactInfos < ActiveRecord::Migration
  def self.up
    create_table :contact_infos do |t|
      t.integer :person_id
      t.timestamps
    end
  end
  def self.down
    drop_table :contact_infos
  end
end

I followed essentially the steps in agile programming in rails version 4, so I am really not sure how to fix this problem. Helps are deeply appreciated!