MongoDB.Driver.DatabaseMetaData.AddUser C# (CSharp) Method

        public void AddUser(string username, string password)
        {
            IMongoCollection users = db["system.users"];
            string pwd = Database.Hash(username + ":mongo:" + password);
            Document user = new Document().Append("user", username).Append("pwd", pwd);
            if (FindUser(username) != null){
                throw new MongoException("A user with the name " + username + " already exists in this database.", null);
            }
            else{
               users.Insert(user);
            }
        }