R4iA - can't cast ActionDispatch::Http::UploadedFile to string

R4iA-chp9error

##Tickets Controller
class TicketsController < ApplicationController
  before_action :require_signin! #except: [:show, :index] (temp-disabled)
  before_action :set_project
  before_action :set_ticket, only: [:show, :edit, :update, :destroy]
  #Restrict Permissions (creating tickets)
  before_action :authorize_create!, only: [:new, :create]
  before_action :authorize_update!, only: [:edit, :update]
  before_action :authorize_delete!, only: :destroy

  def new
   #build instantiates new record for Tickets assocation on Proj obj
    @ticket = @project.tickets.build
    3.times { @ticket.assets.build }
 end

 def create
    @ticket = @project.tickets.build(ticket_params)
    @ticket.user = current_user
    if @ticket.save
      flash[:notice] = "Ticket has been created."
      redirect_to [@project, @ticket]
    else
      flash[:alert] = "Ticket has not been created."
      render action: "new"
    end
 end
 ##(27...52)
private
  def set_project
   @project = Project.find(params[:project_id])
  end

  def set_ticket
    @ticket = @project.tickets.find(params[:id])
  end

  def ticket_params
    params.require(:ticket).permit(:title, :description,
                                  assets_attributes: [:asset])
  end



##SPEC
  scenario "Creating a ticket with an attachment" do
    fill_in "Title", with: "Add documentation for blink tag"
    fill_in "Description", with: "The blink tag has a speed attribute"

    attach_file "File #1", Rails.root.join("spec/fixtures/speed.txt")
    attach_file "File #2", Rails.root.join("spec/fixtures/spin.txt")
    attach_file "File #3", Rails.root.join("spec/fixtures/gradient.txt")

    click_button "Create Ticket"

    expect(page).to have_content("Ticket has been created.")

    within("#ticket .assets") do
      expect(page).to have_content("speed.txt")
      expect(page).to have_content("spin.txt")
      expect(page).to have_content("gradient.txt")
    end
  end 
end

##Form Partial
 <% number = 0 %>
  <%= f.fields_for :assets do |asset| %>
    <p>
    <%= asset.label :asset, "File ##{number += 1}" %>
 
    <%= asset.file_field :asset %>  
    </p>
  <% end %>
  <%= f.submit %>
<% end %>

#Model
class Ticket < ActiveRecord::Base
  belongs_to :project
  belongs_to :user
  validates :title, presence: true
  validates :description, presence: true, length: { minimum: 10 }

  #Defines setter for file uploading
  mount_uploader :asset, AssetUploader
  has_many :assets
  #=>Applies to Ticket's new/build/update-methods
  accepts_nested_attributes_for :assets
end