OfficeTicTacToe.ViewModels.UserViewModel.GetUser C# (CSharp) Method

        internal static UserViewModel GetUser(string userPrincipalName)
        {
            userPrincipalName = userPrincipalName.Trim();
            try
            {
                if (string.IsNullOrEmpty(userPrincipalName))
                    return UserViewModel.Empty;
                UserViewModel user = users.FirstOrDefault(u => u.Email == userPrincipalName || u.UserPrincipalName == userPrincipalName);
                if (user != null)
                    return user;
                user = new UserViewModel()
                {
                    Email = userPrincipalName,
                    UserPrincipalName = userPrincipalName,
                    IsLoadedFromGraph = false,
                };

                users.Add(user);
                return user;
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex.Message);
                throw;
            }
        }