Is it normal to pass null variables from the client side to the service side?

Question

My goal is to create three applications: in WCF, in ASP.NEW Web API and another in WPF.

My question is this::

It is normal, the data that we initialize on the client side namely (WPF) and that we pass to the service (WCF) come to null?

Example of my code - WPF

       InitializeComponent();
       _gestaoInformacao = new Gestao_InformacaoUsersClient();

       newUser = new Utilizador { Username = "Joao" };
       _gestaoInformacao.addNovoUtilizador(newUser);

WCF:

 public void addNovoUtilizador(Utilizador newUser)
    {

        projectContext.Users.Add(newUser);
        projectContext.SaveChanges();
    }

User class:

public class Utilizador
{
    [DataMember]
    [Key]
    private int id_utilizador;

    [DataMember]
    private String _username;

    [DataMember]
    public String Username
    {
        get { return _username; }
        set
        {
            _username = value;
            //OnPropertyChanged("Username");
        }
    }

    [DataMember]
    private String _password;

    [DataMember]
    public String Password
    {
        get { return _password; }
        set
        {
            _password = value;
            //OnPropertyChanged("Password");
        }
    }






}

The point here is that when I pass the Newuser from WPF to WCF and run the debug to see the information you pass, VS says all user data is null (at least the username should have data)

This data, is it normal to be null, or is something wrong? Maybe with Services settings.