association between two models

This is the error I get when I try to fill in the book's form: undefined method 'books' for nil:NilClass & it highlights this line: @book = @owner.books.build(params[:book])

This is what I've done so far:

What am I missing?

Two models: owner and book

Here's the schema

create_table "books", force: :cascade do |t|
  t.string   "title"
  t.string   "isbn"
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
  t.integer  "owner_id"
end

add_index "books", ["owner_id"], name: "index_books_on_owner_id"

create_table "owners", force: :cascade do |t|
  t.string   "first_name"
  t.string   "last_name"
  t.string   "email"
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
 end
end

Here are the models:

class Owner < ActiveRecord::Base
   has_many :books
 end

class Book < ActiveRecord::Base
   belongs_to :owner  
  validates :owner_id, presence: true
 end

This is in book controller:

  def create
   @book = @owner.books.build(params[:book])
     respond_to do |format|
    if @book.save
      format.html { redirect_to @book, notice: 'Book was successfully created.' }
      format.json { render :show, status: :created, location: @book }
    else
     format.html { render :new }
     format.json { render json: @book.errors, status: :unprocessable_entity }
     end
   end
  end

EDIT

This is in the owner's controller:

   def create
      @owner = Owner.new(owner_params)

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

EDIT 2

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

   # Never trust parameters from the scary internet, only allow the white list through.
    def owner_params
      params.require(:owner).permit(:first_name, :last_name, :email, :title, :isbn)
     end

**EDIT 3 **

The method I used in book's controller in create came from this stack