How can I solve this error "Does not allow NULL, Insert Aborted"?

I'm trying to call a stored procedure to make an insert:

private void button1_Click(object sender, EventArgs e)
{
    string connectionString = @"Data Source=******;Initial Catalog=**********;Integrated Security=True";

    using (SqlConnection sqlCon = new SqlConnection(connectionString: connectionString))
    {
        using (SqlCommand cmd = new SqlCommand("InsertAngajat", sqlCon))
        {
            cmd.CommandType = CommandType.StoredProcedure;

            cmd.Parameters.Add("@Nume", SqlDbType.VarChar).Value = textBox1.Text;
            cmd.Parameters.Add("@Prenume", SqlDbType.VarChar).Value = textBox2.Text;
            cmd.Parameters.Add("@DataNasterii", SqlDbType.Date).Value = textBox4.Text;
            cmd.Parameters.Add("@DataAngajare", SqlDbType.Date).Value = DateTime.Today.ToString();
            cmd.Parameters.Add("@cnp", SqlDbType.Char).Value = textBox3.Text.ToCharArray();
            cmd.Parameters.Add("@Localitate", SqlDbType.VarChar).Value = textBox8.Text;
            cmd.Parameters.Add("@Judet", SqlDbType.VarChar).Value = textBox10.Text;
            cmd.Parameters.Add("@Strada", SqlDbType.VarChar).Value = textBox9.Text;
            cmd.Parameters.Add("@Departament", SqlDbType.VarChar).Value = comboBox1.Text;
            cmd.Parameters.Add("@Telefon", SqlDbType.Char).Value = textBox5.Text.ToCharArray();

            if (checkBox1.Checked) 
                cmd.Parameters.Add("@Sex", SqlDbType.Char).Value = 'M';
            else if (checkBox2.Checked) 
                cmd.Parameters.Add("@Sex", SqlDbType.Char).Value = 'F';
            else 
                MessageBox.Show("Nu a fost bifat sexul");

            cmd.Parameters.Add("@Numar", SqlDbType.Int).Value = Convert.ToInt32(textBox11.Text);
            cmd.Parameters.Add("@Salariu", SqlDbType.Int).Value = Convert.ToInt32(textBox6.Text);

            sqlCon.Open();
            cmd.ExecuteNonQuery();
        }
    }

    this.Close();  
}

But this is the error I get when I press the button and save everything.

https://i.sstatic.net/TTntF.png

This is the SQL Server stored procedure:

ALTER PROCEDURE [dbo].[InsertAngajat] 
    @Nume VARCHAR(50), 
    @Prenume VARCHAR(50),
    @Departament VARCHAR(50),
    @cnp CHAR(13),
    @DataNasterii DATE,
    @Telefon VARCHAR(12) = "NONE",
    @DataAngajare DATE,
    @Salariu INT,
    @Sex CHAR(1) = 'F',
    @Judet VARCHAR(50),
    @Localitate VARCHAR(50),
    @Strada VARCHAR(50),
    @Numar INT
AS
BEGIN
    SET NOCOUNT ON;

    DECLARE @DepID INT = (SELECT D.DepartamentID 
                          FROM Departamente D 
                          WHERE D.[Nume Departament] = @Departament);

    INSERT INTO [dbo].Angajat (Nume, Prenume, DepartamentID, CNP, DataNasterii,
                               Telefon, DataAngajarii, Salariu, Sex, Localitate,
                               [Sector/Judet], Strada, nr)
    VALUES (@Nume, @Prenume, @DepID, @cnp, @DataNasterii,
            @Telefon, @DataAngajare, @Salariu, @Sex, @Localitate,
            @Judet, @Strada, @Numar)        
END

I made sure that the text boxes were having data. I have no idea what else to try.

I'm expecting that as long as the values in the text boxes aren't NULL to be able to Insert all their data easily.