If question IF no have value (NULL),then set o to textbox SQL

I try this, but when is value from sql NULL, nothing hapend, need to be 0.00 when is NULL

private void ukupno_bez_pdv_usluge()
{
SqlConnection con2 = new SqlConnection(cs);

string sqlquery = ("SELECT SUM(isnull(cast(REPLACE(TRY_CONVERT(int,TRY_CONVERT(float,iznos_bpdv),1), '#,0.00','')AS decimal(10,2)),0.00)) as UKUPNObpdv," +
" SUM(isnull(cast(REPLACE(TRY_CONVERT(float, TRY_CONVERT(float, pdv), 1), '#,0.00', '')AS decimal(10, 2)), 0.00)) as UKUPNOpdv," +
" SUM(isnull(cast(REPLACE(TRY_CONVERT(float, TRY_CONVERT(float, mp_cijena), 1), '#,0.00', '')AS decimal(10, 2)), 0.00)) as UKUPNOsapdv" +
" from mp_racun_roba" +
" where tip_robe = 'Usluge (Generalno)' and id_fakture =" + id_fakture
);

SqlCommand command = new SqlCommand(sqlquery, con2);
con2.Open();
SqlDataReader sdr = command.ExecuteReader();

if (sdr.Read())
{

usluga_bez_pdvTextBox.Text = sdr["UKUPNObpdv"].ToString();
usluga_pdvTextBox.Text = sdr["UKUPNOpdv"].ToString();
usluga_sa_pdvTextBox.Text = sdr["UKUPNOsapdv"].ToString();

}
else
{

usluga_bez_pdvTextBox.Text = "0.00";
usluga_pdvTextBox.Text = "0.00";
usluga_sa_pdvTextBox.Text = "0.00";

}
con2.Close();
}