неопределенный метод `first_name' для ошибки nil:NilClass

Я пытаюсь установить связь между моделями user и shipment. Я использую [devise][1] для генерации users все прошло хорошо, но теперь я остановился на этом. Я получаю эту ошибку:

undefined method `first_name' for nil:NilClass

Мои модели

Доставка.rb

class Shipment < ActiveRecord::Base
  belongs_to :user
end

User.rb

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable
end

Мои контроллеры

Shipments_Controller.rb

class ShipmentsController < ApplicationController
  before_action :set_shipment, only: [:show, :edit, :update, :destroy]

  # GET /shipments
  # GET /shipments.json
  def index
    @shipments = Shipment.all
  end

  # GET /shipments/1
  # GET /shipments/1.json
  def show
  end

  # GET /shipments/new
  def new
    @shipment = Shipment.new
  end

  # GET /shipments/1/edit
  def edit
  end

  # POST /shipments
  # POST /shipments.json
  def create
    @shipment = Shipment.new(shipment_params)

    respond_to do |format|
      if @shipment.save
        format.html { redirect_to @shipment, notice: 'Shipment was successfully created.' }
        format.json { render :show, status: :created, location: @shipment }
      else
        format.html { render :new }
        format.json { render json: @shipment.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /shipments/1
  # PATCH/PUT /shipments/1.json
  def update
    respond_to do |format|
      if @shipment.update(shipment_params)
        format.html { redirect_to @shipment, notice: 'Shipment was successfully updated.' }
        format.json { render :show, status: :ok, location: @shipment }
      else
        format.html { render :edit }
        format.json { render json: @shipment.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /shipments/1
  # DELETE /shipments/1.json
  def destroy
    @shipment.destroy
    respond_to do |format|
      format.html { redirect_to shipments_url, notice: 'Shipment was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_shipment
      @shipment = Shipment.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def shipment_params
      params.require(:shipment).permit(:user_id, :description, :from, :to, :date, :pay)
    end
end

Мои файлы миграции БД:

devise_create_users.rb

class DeviseCreateUsers < ActiveRecord::Migration
  def change
    create_table(:users) do |t|

      t.string :first_name
      t.string :last_name
      t.string :city_name

      t.string :email,              null: false, default: ""
      t.string :encrypted_password, null: false, default: ""

      ## Recoverable
      t.string   :reset_password_token
      t.datetime :reset_password_sent_at

      ## Rememberable
      t.datetime :remember_created_at

      ## Trackable
      t.integer  :sign_in_count, default: 0, null: false
      t.datetime :current_sign_in_at
      t.datetime :last_sign_in_at
      t.string   :current_sign_in_ip
      t.string   :last_sign_in_ip

      ## Confirmable
      # t.string   :confirmation_token
      # t.datetime :confirmed_at
      # t.datetime :confirmation_sent_at
      # t.string   :unconfirmed_email # Only if using reconfirmable

      ## Lockable
      # t.integer  :failed_attempts, default: 0, null: false # Only if lock strategy is :failed_attempts
      # t.string   :unlock_token # Only if unlock strategy is :email or :both
      # t.datetime :locked_at


      t.timestamps null: false
    end

    add_index :users, :email,                unique: true
    add_index :users, :reset_password_token, unique: true
    # add_index :users, :confirmation_token,   unique: true
    # add_index :users, :unlock_token,         unique: true
  end
end



add_user_id_to_shipment.rb
class AddUserIdToShipments < ActiveRecord::Migration
  def change
    add_column :shipments, :user_id, :integer
    add_index :shipments, :user_id
    remove_column :shipments, :name
  end
end

Мои файлы просмотров отправлений:

_form.html.erb

<%= simple_form_for(@shipment, html: {class: "form-horizontal"}) do |f| %>
  <% if @shipment.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@shipment.errors.count, "error") %> prohibited this shipment from being saved:</h2>

      <ul>
      <% @shipment.errors.full_messages.each do |message| %>
        <li><%= message %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <%= f.input :user_id %>
  <%= f.input :description %>

  <div class="field">
    <%= f.label :ship_from %><br>
    <%= f.select :from, ['New York']%>
  </div>

  <div class="field">
    <%= f.label :ship_to %><br>
        <%= f.select :to, [ 'New york', 'Orlanda' ] %>
  </div>
    <%= f.input :date %>
    <%= f.input :pay %>
  <div class="form-actions">
    <%= f.button :submit %>
  </div>
<% end %>

Index.html.erb

<div class="page-header">
<h1>Listing Shipments</h1>
</div>

<%= link_to "Post a new Shipment", new_shipment_path, class: "btn btn-success" %>

<% @shipments.each do |shipment| %>
<div class="shipment">
  <h3><strong><%= shipment.user.first_name %></strong></h3>
  <h5><strong>DESCRIPTION: </strong><%= shipment.description %></h5>
  <div class="meta">
    <%= link_to time_ago_in_words(shipment.created_at) + " ago" %> |
    <%= link_to "show", shipment %>
    <span class="admin"> 
        | <%= link_to "Edit", edit_shipment_path(shipment) %> |
        <%= link_to "Delete", shipment, method: :delete, data: { confirm: "Are you sure?"} %>
  </span>
    </div>
  </div>
  <% end %>

Show.html.erb ‹%= уведомление %>

<p>
  <strong>Name:</strong>
  <%= @shipment.user.first_name %>
</p>

<p>
  <strong>Shipment Description:</strong>
  <%= @shipment.description %>
</p>

<p>
  <strong>Shipment From:</strong>
  <%= @shipment.from %>
</p>

<p>
  <strong>Ship To:</strong>
  <%= @shipment.to %>
</p>

<p>
  <strong>Shipment Date:</strong>
  <%= @shipment.date %>
</p>

<p>
  <strong>Pay:</strong>
  <%= @shipment.pay %>
</p>

<%= link_to 'Edit', edit_shipment_path(@shipment) %> |
<%= link_to 'Back', shipments_path %>

Моя командная строка показывает этот журнал:

Started GET "/" for ::1 at 2015-07-28 16:07:24 +0530
Processing by ShipmentsController#index as HTML
  Shipment Load (0.0ms)  SELECT "shipments".* FROM "shipments"
  User Load (0.0ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT
 1  [["id", 1]]
  Rendered shipments/index.html.erb within layouts/application (0.0ms)
Completed 500 Internal Server Error in 16ms (ActiveRecord: 0.0ms)

ActionView::Template::Error (undefined method `first_name' for nil:NilClass):
     6:
     7: <% @shipments.each do |shipment| %>
     8: <div class="shipment">
     9:   <h3><strong><%= shipment.user.first_name %></strong></h3>
    10:   <h5><strong>DESCRIPTION: </strong><%= shipment.description %></h5>
    11:   <div class="meta">
    12:         <%= link_to time_ago_in_words(shipment.created_at) + " ago" %> |

  app/views/shipments/index.html.erb:9:in `block in _app_views_shipments_index_h
tml_erb__634505161_51269712'
  app/views/shipments/index.html.erb:7:in `_app_views_shipments_index_html_erb__
634505161_51269712'


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