using static System.Console;

​

public class Program {

     public static void Main(string[] args) {

         var client = new string[7, 7];

         InsertData<ClientHeader>(client);

         InsertData<ClientHeader>(client);

         AlunoLista(client);

     }

    static int getInsertIndex(string[,] matrix) {

        for (int j = 0; j < matrix.GetLength(0); j++) if (string.IsNullOrEmpty(matrix[j, 0])) return j;

        return -1;

    }

    private static void InsertData<T>(string[,] matrix) {

        int n = getInsertIndex(matrix), id = 1;

        matrix[n, 0] = (id++).ToString();

        int x = matrix.GetLength(1) - 1;

        matrix[n, x] = "true";

        for (var j = 1; j < matrix.GetLength(1); j++) {

            do {

                Write($"\nInsert {GetHeader<T>(j)}: ");

                matrix[n, j] = ReadLine();

            } while (string.IsNullOrEmpty(matrix[n, j]));

        }

    }

​

    private static string GetHeader<T>(int i) => System.Enum.GetName(typeof(T), i);

​

    static void AlunoLista(string[,] lista) {

        var linha = new string('-', 49);

        int[] tamanho = new int[] { 4, 10, 10, 20, 10, 10, 10 };

        for (int i = 0; i < lista.GetLength(1); i++) {

            WriteLine($"{linha}|");

            for (int j = 0; j < lista.GetLength(0); j++) {

                lista[j, i] = lista[j, i] ?? "";  // <===================== mudei aqui

                var espaço = new string (' ', tamanho[j] - lista[j, i].Length);

                Write($"{lista[j, i]}{espaço}|");

            }

            WriteLine();

        }

        WriteLine(linha);

    }

    enum ClientHeader { Id, Name, Surname, Addres, CodPostal, Telephone, Email, State };

}