Builder without parameters is not working, is leaving the object as null [closed]

I have a class with two constructors. The empty constructor (no arguments) is not working. The program does not display an error. One of the constructors receives the parameters nome and limitedecredito ; and another, empty, initializes CPF .

It turns out that the cpf (TCPF) field is getting the value NULL .

Client class constructor:

public Cliente():base()
{ 
}

Main Program:

(...)
case 1:
    Console.Clear();
    c1 = new Cliente();
    Console.Write("CPF:");
    CPF = Console.ReadLine();
    if (c1.setCPF(CPF) == false)
    {
        Console.WriteLine("CPF inválido");
        Console.ReadKey();
        break;
    }
    Console.Write("Nome:");
    string nome = Console.ReadLine();
    Console.Write("Limite de credito R$:");
    double limitecredito = double.Parse(Console.ReadLine());
    c1 = new Cliente(nome, limitecredito);
    LC.Add(c1);
    Console.Write("Cadastro realizado com sucesso");
    Console.ReadKey();
    break;
(...)

Class Cliente :

private double limitecredito;

public Cliente():base()
{ 
}

public Cliente(string n, double limitec) : base(n)
{
    limitecredito = limitec;
}

Class Pessoa (Mother):

private string nome;
private TCPF cpf;

public Pessoa()
{
    cpf = new TCPF();
}

public Pessoa(string n)
{
    cpf = new TCPF();
    nome = n;
}

public string Nome
{
    get { return nome; }
}

public bool setCPF(string X)
{
    return cpf.ValidaCpf(X);
}

public string Cpf
{
    get { return cpf.Cpf; }
}