current_user helper method error

[AjayBarot]

hi i m using rails 4 and i have this error shows in current_user helper method .

ActiveRecord::RecordNotFound in UsersController#new
Couldn't find User without an ID
and My code for pplication_controller.rb:
def current_user
@current_user ||= User.find(session[:user_id]) if session [:user_id]
end
and this is my code of user_controller.rb:
def new
@user= User.new
end
def create
@user= User.new(params[:user])
if @user.save
redirect_to root_url, :notice => "Signed up!"
else
render "new"
end
end
and now this is my code for application.html.erb where i check current_user:

<% if current_user %> Logged in as <%= current_user.email %>, <%= link_to "Log out", log_out_path %> <% else %> <%= link_to "Sign up", sign_up_path %> <%= link_to "log in", log_in_path %> <% end -%>

Screenshot