Error with shared examples rspec, always return undefined method id for nil class

reviews_controller_spec.rb

require 'spec_helper'

describe ReviewsController do
  before(:each) do
    signin_user
    @video = Fabricate(:video)
  end
  describe 'Post Create' do
    context 'Authenticated user Valid data' do
      it 'create a new review with valid data' do
        expect{
          post :create, review: {rating: "1", description: "icdgivbwi"}, video_id: @video.id
        }.to change(Review,:count).by(1)
      end
      it 'will redirect_to video show after creation' do
        post :create, review: {rating: "1", description: "icdgivbwi"}, video_id: @video.id
        expect(response).to redirect_to video_path(@video)
      end
      it 'will fill flash[:info] variable' do
        post :create, review: {rating: "1", description: "icdgivbwi"}, video_id: @video.id
        expect(flash[:info]).to_not be_empty
      end
    end

    context 'Authenticated user Invalid data' do
      it 'will not create a review' do
        expect{
          post :create, review: {rating: "1"}, video_id: @video.id
        }.to_not change(Review,:count)
      end
      it 'will render videos show' do
        post :create, review: {rating: "1"}, video_id: @video.id
        expect(response).to render_template 'videos/show'
      end
      it 'will fill flash[:danger] variable' do
        post :create, review: {rating: "1"}, video_id: @video.id
        expect(flash[:danger]).to_not be_empty
      end
    end


    it_behaves_like "unauthenticated user" do
      let(:action) { post :create, review: {rating: "1", description: "icdgivbwi"}, video_id: @video }
    end

  end
end

shared_examples.rb

shared_examples "unauthenticated user" do
  it "redirect to sigin page if you are not log in" do
    logout_user
    action
    expect(response).to redirect_to signin_path
  end
end