private AVUser warpUser(string userId = null, AVUser user = null)
 {
     if (user == null)
     {
         if (string.IsNullOrEmpty(userId))
         {
             throw new ArgumentNullException("team id and team can NOT both be null at the same time");
         }
         user = AVUser.CreateWithoutData <AVUser>(userId);
     }
     return(user);
 }