undefined method `downcase' for nil:NilClass railstutorial - ruby-on-rails

Question

I try railstutorial rails4.0
now 9.2.0 and no Rspec error.
but rails s has NoMethodError in Users#index when open /users
why?
app / models / user.rb
class User < ActiveRecord::Base
before_save { self.email = email.downcase }
before_create :create_remember_token
validates :name, presence: true, length: { maximum: 50 }
VALID_EMAIL_REGEX = /\A[\w+\-.]+#[a-z\d\-]+(\.[a-z]+)*\.[a-z]+\z/i
validates :email, presence: true, format: { with: VALID_EMAIL_REGEX },
uniqueness: { case_sensitive: false }
has_secure_password
validates :password, length: { minimum: 6 }
def User.new_remember_token
SecureRandom.urlsafe_base64
end
def User.encrypt(token)
Digest::SHA1.hexdigest(token.to_s)
end
private
def create_remember_token
self.remember_token = User.encrypt(User.new_remember_token)
end
end
app / controllers / users_controller.rb
class UsersController < ApplicationController
before_action :signed_in_user, only: [:index, :edit, :update]
before_action :correct_user, only: [:edit, :update]
def index
#users = User.all
end
def show
#user = User.find(params[:id])
end
def new
#user = User.new
end
def create
#user = User.new(user_params)
if #user.save
sign_in #user
flash[:success] = "Welcome to the Sample App!"
redirect_to #user
else
render 'new'
end
end
def edit
end
def update
if #user.update_attributes(user_params)
flash[:success] = "Profile updated"
redirect_to #user
else
render 'edit'
end
end
private
def user_params
params.require(:user).permit(:name, :email, :password, :password_confirmation)
end
#Before actions
def signed_in_user
unless signed_in?
store_location
redirect_to signin_url, notice: "Please sign in."
end
end
def correct_user
#user = User.find(params[:id])
redirect_to(root_path) unless current_user?(#user)
end
end
app / views / users / index.html.slim
- provide(:title, 'All users')
h1 All users
ul.users
- #users.each do |user|
li
= gravatar_for user, size: 52
= link_to user.name, user
app / helpers / users_helper.rb
module UsersHelper
# Returns the Gravatar (http://gravatar.com/) for the given user.
def gravatar_for(user, options = { size: 50 })
gravatar_id = Digest::MD5::hexdigest(user.email.downcase)
size = options[:size]
gravatar_url = "https://secure.gravatar.com/avatar/#{gravatar_id}?s=#{size}"
image_tag(gravatar_url, alt: user.name, class: "gravatar")
end
end

Answer 1

I have not tried. but it can be something like this.
before_save { self.email = email.downcase if email}

Answer 2

Your error would seem to be coming from the first line of the gravatar_for method, which calls user.email.downcase, suggesting you have at least one user with a nil email address in the database.