undefined method `new_record?' for nil:NilClassを解決したいです。

新規投稿画面と編集画面を部分テンプレートで作成し
submitボタンの表示する文字をファイルによって変えたいです。新規投稿時はCreateBook、編集の時はUpdateBookが表示されるようにしたいです。

その際あるサイト(https://teratail.com/questions/312875)を参考に

_form.html.erb

RubyonRails
<% if f.object.new_record? %>
      <%= f.submit "Create Book", class: "btn btn-success" %>
    <% else %>
      <%= f.submit "Update Book", class: "btn btn-success" %>
    <% end %>

を記述した所、userのshow.html.erb(userの詳細ページ)でエラーが発生しました

(サイトにあるようにnew_record?メソッドを自分で定義する必要は無いと思います)
(新規投稿のページや投稿を編集するページではエラーは発生していません)

発生している問題・エラーメッセージ

NoMethodError in Users#show
Showing /home/ec2-user/environment/bookers2-debug/app/views/books/_form.html.erb where line #21 raised:

undefined method `new_record?' for nil:NilClass
Extracted source (around line #21):
19
20
21
22
23
24

<% if f.object.new_record? %>
   <%= f.submit "Create Book", class: "btn btn-success" %>
 <% else %>
   <%= f.submit "Update Book", class: "btn btn-success" %>

Trace of template inclusion: app/views/users/show.html.erb

Rails.root: /home/ec2-user/environment/bookers2-debug

Application Trace | Framework Trace | Full Trace
app/views/books/_form.html.erb:21:in block in _app_views_books__form_html_erb__3555135995817864763_70203137971340' app/views/books/_form.html.erb:1:in _app_views_books__form_html_erb__3555135995817864763_70203137971340'
app/views/users/show.html.erb:8:in `_app_views_users_show_html_erb___123336745112956188_70203137756200'
Request
Parameters:

{"id"=>"1"}
Toggle session dump
Toggle env dump
Response
Headers:

None

該当のソースコード

books/_form.html.erb

RubyonRails
<%= form_with model:book,local:true do |f| %>
  <div class="form-group">
    <%= f.label :title %>
    <%= f.text_field :title, class: 'form-control book_title' %>
  </div>
  <div class="form-group">
    <%= f.label :opinion %>
    <%= f.text_area :body, class: 'form-control book_body' %>
  </div>
  <div class="form-group">
 <% if f.object.new_record? %>
      <%= f.submit "Create Book", class: "btn btn-success" %>
    <% else %>
      <%= f.submit "Update Book", class: "btn btn-success" %>
    <% end %>
  </div>
<% end %>

user/show.html.erb

RubyonRails
<div class='container px-5 px-sm-0'>
  <div class='row'>
    <div class='col-md-3'>
      <h2>User info</h2>
      <%= render 'info', user: @user %>
      <h2 class="mt-3">New book</h2>
      <%= render 'books/form', book: @book_form %>
    </div>
    <div class='col-md-8 offset-md-1'>
      <h2>Books</h2>
      <%= render 'books/index',books: @books %>
    </div>
  </div>
</div>

books_controller.rb

RubyonRails
class BooksController < ApplicationController
before_action :correct_user, only: [:edit, :update]
def show
    @book_form = Book.new
    @book = Book.find(params[:id])
    @user = @book.user
  end

  def index
    @books = Book.all
    @book = Book.new

  end

  def create
    @book = Book.new(book_params)
    @book.user_id = current_user.id
    if @book.save
      redirect_to book_path(@book), notice: "You have created book successfully."
    else
      @books = Book.all
      render 'index'
    end
  end

  def edit
    @book = Book.find(params[:id])

  end



  def update
    @book = Book.find(params[:id])
    if @book.update(book_params)
      redirect_to book_path(@book), notice: "You have updated book successfully."
    else
      render "edit"
    end
  end

  def destroy
    @book = Book.find(params[:id])
    @book.destroy
    redirect_to books_path
  end

  private

  def book_params
    params.require(:book).permit(:title, :body)
  end

  def correct_user
    @book = Book.find(params[:id])
    @user = @book.user
    redirect_to(books_path) unless @user == current_user
  end

end

users_controller.rb

RubyonRails
class UsersController < ApplicationController

 
  before_action :ensure_correct_user, only: [:update, :edit]



  def show
    @user = User.find(params[:id])
    @books = @user.books
    @book = Book.new
  
  end

  def index
    @users = User.all
    @book = Book.new
    
  end

  def edit
    @user = User.find(params[:id])
  end

  def update
    if @user.update(user_params)
      redirect_to user_path(@user), notice: "You have updated user successfully."
    else
       @user = User.find(params[:id])
       @books = @user.books
       @book = Book.new
      render "show"
    end
  end

  private
    def user_params
      params.require(:user).permit(:name, :introduction, :profile_image)
    end

   
    def ensure_correct_user
      @user = User.find(params[:id])
      unless @user == current_user
        redirect_to user_path(current_user)
      end
    end

  end

models/book.rb

RubyonRails
class Book < ApplicationRecord
	belongs_to :user

	validates :title, presence: true
	validates :body, presence: true, length: {maximum: 200}
end

models/user.rb

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

  has_many :books
  attachment :profile_image, destroy: false

  validates :name, length: {maximum: 20, minimum: 2}, uniqueness: true
  validates :introduction, length: {maximum: 50}

end