Polymorphic associations do not support computing the class

main.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails', '7.0.3'  # use correct rails version
  gem 'cancancan', '3.4.0' # use correct cancancan version
  gem 'sqlite3' # use another DB if necessary
end

require 'active_record'
require 'action_controller'
require 'cancancan'
require 'cancan/model_adapters/active_record_adapter'
require 'cancan/model_adapters/sti_normalizer'
require 'cancan/model_adapters/conditions_normalizer'
require 'cancan/model_adapters/conditions_extractor'
require 'cancan/model_adapters/active_record_4_adapter'
require 'cancan/model_adapters/active_record_5_adapter'
require 'minitest/autorun'
require 'logger'

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

# create your tables here
ActiveRecord::Schema.define do
  create_table :comments, force: true  do |t|
    t.integer  :imageable_id
    t.string  :imageable_type
    t.integer :user_id
  end

  create_table :users, force: true  do |t|
    t.string :name
  end
end

class Comment < ActiveRecord::Base
  belongs_to :commentable, polymorphic: true
  belongs_to :user
end

class User < ActiveRecord::Base
  has_many :comments
end

class Ability
  include CanCan::Ability

  def initialize(user)
    can :read, Comment, user_id: user.id
  end
end

class TestApp < Rails::Application
  config.root = File.dirname(__FILE__)
  config.session_store :cookie_store, key: "cookie_store_key"
  secrets.secret_token    = "secret_token"
  secrets.secret_key_base = "secret_key_base"

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger

  routes.draw do
    resources :comments, only: [:index]
  end
end

class CommentsController < ActionController::Base
  include CanCan::ControllerAdditions

  load_resource :user, class: 'User'
  load_and_authorize_resource through: :user, only: [:index], class: 'Comment'

  def current_user
    User.first
  end

  def index
    head :no_content
  end
end

class CommentsControllerTest < ActionController::TestCase
  setup do
    @controller = CommentsController.new
    @routes = Rails.application.routes

    @user1 = User.create!
    comment = Comment.create(user_id: @user1.id)
  end

  def test_action
    get :index, params: { user_id: @user1.id }
  end
end