def wf_user_id?(user)
      return true if user.is_a?(String) && user.length < 256 && !user.empty?
      raise Wavefront::Exception::InvalidUserId
    end
def wf_user_id?(user)
      return true if user.is_a?(String) && user.length < 256 && !user.empty?
      raise Wavefront::Exception::InvalidUserId
    end
Ensure the given argument is a valid user.

 @param user [String] user identifier
 @return true if valid
 @raise Wavefront::Exceptions::InvalidUserId if not valid