def role= role
      raise ArgumentError, '#add_role takes a single role String or Symbol as the argument' if !role || role.kind_of?(Array)
      self.roles = role
    end
def role= role
      raise ArgumentError, '#add_role takes a single role String or Symbol as the argument' if !role || role.kind_of?(Array)
      self.roles = role
    end
set a single role