why my datagridview produce duplicate data on user cell_click inside the datagridview in c#

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C#

why my datagridview produce duplicate data on user cell_click inside the datagridview in c#

i use the following code,but it does not pass values to the textbox in the user form fro the datagridview and give me this Error in the folowing statement;
Statement:txtusername.text=dr.Cells[0].Value.ToString();

Error:
"An unhandled exception of type 'System.NullReferenceException' occurred in Company Accounts.exe

Additional information: Object reference not set to an instance of an object."

///this is my formuserslection code.
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
 
namespace Company_Accounts
{
    public partial class FrmUserSelection : Form
    {
        DataSet ds = null; // Set null here
        public FrmUserSelection()
        {
            InitializeComponent();
           
        }
 
        private void FrmUserSelection_Load(object sender, EventArgs e)
        {
            
            fillgrid();
            ControlBox = false;
            usdgv.Columns[0].SortMode = DataGridViewColumnSortMode.NotSortable;
            txtwildsearch.Focus();
            //this.usdgv.Columns["Password"].Visible = false;
            
        }
 
        private void fillgrid()
        {
            ds=new DataSet(); //Create new obj here
            ConnectionString.cnn.Open();
            SqlDataAdapter da = new SqlDataAdapter("select username as [User Name],Password,Title, userrole,logincomputer as [Login Computer] ,logindate as [Login Date] ,Logintime as [Login Time] from login", ConnectionString.cnn);
            da.Fill(ds, "tbl_login");
            usdgv.DataSource = ds.Tables["tbl_login"];
            ConnectionString.cnn.Close();
        }
 
        private void usdgv_CellMouseDoubleClick(object sender, DataGridViewCellMouseEventArgs e)
        {
            FrmUser.dr = usdgv.CurrentRow;
            fillgrid();
            this.Close();
        }
 
        private void btnwildsearch_Click(object sender, EventArgs e)
        {
            FrmUser.dr = usdgv.CurrentRow;
            this.Close();
        }
 
        private void usdgv_CellClick(object sender, DataGridViewCellEventArgs e)
        {
            label1.Text ="" +usdgv.Columns[usdgv.CurrentCell.ColumnIndex].HeaderText + " ";
            s1.Text = "" + usdgv.Columns[usdgv.CurrentCell.ColumnIndex].HeaderText + " ";
            s2.Text = "" + usdgv.Columns[usdgv.CurrentCell.ColumnIndex].HeaderText + " ";
            s3.Text = "" + usdgv.Columns[usdgv.CurrentCell.ColumnIndex].HeaderText + " ";
        }
 
        private void txtwildsearch_TextChanged(object sender, EventArgs e)
        {
            DataView dt = ds.Tables[0].DefaultView;
            string tbcolumn;
            try
            {
                tbcolumn = usdgv.Columns[usdgv.CurrentCell.ColumnIndex].HeaderText.ToString();
                dt.RowFilter = string.Format("" + tbcolumn + " ='{0}'", txtwildsearch.Text);
                if (dt.Count > 0)
                {
                    usdgv.DataSource = dt; 
                }
                else
                {
                    usdgv.DataSource = 0;                    
                }
                if (usdgv.RowCount == 0)
                {
                    usdgv.DataSource = ds.Tables[0].DefaultView; 
                }
            }
            catch (Exception)
            { 
            }
        }
    }
}

////and this is the user form code.

public static DataGridViewRow dr;
        FrmUserSelection fus = new FrmUserSelection();
        private void btnsearch_Click(object sender, EventArgs e)
        {
            DataCollection();

            
        }

private void DataCollection()
       {
           fus.ShowDialog();
           txtusername.Text = dr.Cells[0].Value.ToString();
           txtpassword.Text = dr.Cells[1].Value.ToString();
           txttitle.Text = dr.Cells[2].Value.ToString();
           txtuserrole.Text = dr.Cells[3].Value.ToString();
           txtlogincmpt.Text = dr.Cells[4].Value.ToString();
           txtlogindate.Text = dr.Cells[5].Value.ToString();
           txtlogintime.Text = dr.Cells[6].Value.ToString();
           disable();
           txtusername.Enabled = false;
           btnedit.Enabled = true;
           btndelete.Enabled = true;
       }