old_contents: export default {
  	destroy () {},
  	reveal () {},
  	sync () {},
  	get noop () { return true },
  }
  
new_contents: export default {
  	clean () {},
  	destroy () {},
  	reveal () {},
  	sync () {},
  	get noop () { return true },
  }
  
subject: add clean method to noop instance