what is wrong with my before filter

ChaptersController.rb

class ChaptersController < ApplicationController
  before_filter :check_ownership_of_chapters_book
  
  def check_ownership_of_chapters_book
    #abort(params.to_yaml)
    
=begin
    ---
    utf8: ✓
    authenticity_token: NwsHY5ex9ynzXfDSXiQ8EBps6Yhzxf0iPPbJPWLkTtg=
    chapter:
      title: test
      content: ''
      book_id: '1'
    action: create
    controller: chapters
    book_id: '1'
=end
    
    if Book.find(params[:book_id]).author != current_user
      flash[:error] = "You are not the author of the book you are adding the chapter to"
      redirect_to root_url
    end
    
# Couldn't find Book without an ID

# how come when when the params have book_id: '1' ?
    
  end