nil：NilClass的未定义方法“读取”

当我尝试通过电子邮件发送上载的附件时，为什么会得到nil：NilClass的未定义方法“ read”？

listings_controller.rb

def send_resume_email
  @listing = Listing.find(params[:id])
  @user = User.find_by_id(params[:id])
  UserMailer.new_resume(params[:resume].read(), params[:resume].original_filename, @user, @listing).deliver
  redirect_to findjobs_path, notice: 'Message sent'
end

user_mailer.rb

def new_resume(user, listing, file, filename)
  @listing = listing
  @user = user
  attachments[filename] = file
  @url = 'http://www.new.com'
  mail(to: listing.user.email, subject: 'Thanks for the awesome site')
end

非常感谢您的帮助。