def roles=(*role_names)
      role_names = role_names.flat_uniq
      role_names = extract_roles(role_names)
      return nil if role_names.empty?
      set_roles(select_valid_roles role_names)
    end
def roles=(*role_names)
      role_names = role_names.flat_uniq
      role_names = extract_roles(role_names)
      return nil if role_names.empty?
      set_roles(select_valid_roles role_names)
    end
assign multiple roles