want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object"

{
                    string query = "Select * from Guaronters where Guarantor_CNIC='" + cbocnic1.Text + "-" + cbocnic2.Text + "-" + cbocnic3.Text + "'";
                   // MessageBox.Show(query);
                    SqlDataAdapter da = new SqlDataAdapter(query, cn);
                  dt = new DataTable();



                    da.Fill(dt);


                    if (dt.Rows.Count == 0)
                    {
                        MessageBox.Show("The CNIC'" + cbocnic1.Text + "-" + cbocnic2.Text + "-" + cbocnic3.Text + "'does not Exists!!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                        cbocnic1.SelectAll();
                        cbocnic1.Focus();
                    }
                    else
                    {
                      r = 0;
                        Displayrecord();
                   }



                    }
                }
        }

                   public void Displayrecord()

                    {

                       Guarantor_Search gse = new Guarantor_Search();

                        gse.txtname.Text = dt.Rows[r]["Name"].ToString();
                        gse.txtfather.Text = dt.Rows[r]["Father_name"].ToString();
                        gse.txthusband.Text = dt.Rows[r]["Husband_name"].ToString();
                        gse.dateTimePicker1.Value = Convert.ToDateTime(dt.Rows[r]["Date_of_Birth"]);
                        gse.txtmarital.Text = dt.Rows[r]["Marital_Status"].ToString();
                        gse.txtoccupation.Text = dt.Rows[r]["Occupation"].ToString();
                        gse.txtpostal.Text = dt.Rows[r]["Postal_address"].ToString();


                        string str;
                        str = dt.Rows[r]["Customer_CNIC"].ToString();
                        string[] cnic1;
                        cnic1 = str.Split('-');
                        gse.txtcustomercnic1.Text = cnic1[0];
                        gse.txtcustomercnic2.Text = cnic1[1];
                        gse.txtcustomercnic3.Text = cnic1[2];

                        string str1;
                        str1 = dt.Rows[r]["Mobile"].ToString();
                        string[] Mobile;
                        Mobile = str1.Split('-');
                        gse.txtcode.Text = Mobile[0];
                        gse.txtmobile.Text = Mobile[1];

                        string str2;
                        str2 = dt.Rows[r]["Guarantor_CNIC"].ToString();
                        string[] cnic;
                        cnic = str2.Split('-');
                        gse.txtcnic1.Text = cnic[0];
                        gse.txtcnic2.Text = cnic[1];
                        gse.txtcnic3.Text = cnic[2];




                        if (dt.Rows[r]["Gender"].ToString() == "Male")
                        {
                            gse.rdomale.Checked = true;
                        }
                        else
                        {
                            gse.rdofemale.Checked = true;


                        }
                        gse.Show();

       }

                    public void nextrecord()
                    {
                        if (r < dt.Rows.Count - 1)
                        {
                            r = r + 1;
                            Displayrecord();
                        }
                        else
                        {
                            MessageBox.Show("You are at Last Record");
                        }

                    }

private void button2_Click(object sender, EventArgs e)
      {
          gseup.nextrecord();



      }