def people_scope
    @account ? @account.people : Person
  end

  def find_person(key = :id)
    @person  = people_scope.find_by_id(params[key])
    raise NotFound unless @person
  end

  # or

  def find_folder(key = :id)
    @folder = Folder.find_by_id(params[key])
    raise NotFound unless @folder
  end

  def build_folder(key = :folder)
    @folder = folders_scope.new(params[key])
  end

  def folders_scope
    @project ? @project.folders : Folder
  end