How to handle Null Reference Exception error of DropDownList Item selection in ASP.Net

I am having this exception while running the code. Please check and let me know what I am missing here. I am providing the lines of code below. I am having the error at these line.

string breach_reason = (e.Row.FindControl("lblbreach") as Label).Text; ddlbreachreason.Items.FindByValue(breach_reason).Selected = true;

Thanks,

Srivatsan Srinivasan.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Configuration;
using System.Data.SqlClient;

public partial class _Default : Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            Lblnotification.Text = "Please click the checkbox to edit the Gridview";
            this.BindGrid();

        }
    }

    private void BindGrid()
    {
        SqlCommand cmd = new SqlCommand("select * from Incident_Details");
        GVData.DataSource = this.ExecuteQuery(cmd, "SELECT");
        GVData.DataBind();
    }

    private DataTable ExecuteQuery(SqlCommand cmd, string action)
    {
        string conString = ConfigurationManager.ConnectionStrings["Constring"].ConnectionString;
        using (SqlConnection con = new SqlConnection(conString))
        {
            cmd.Connection = con;
            switch (action)
            {
                case "SELECT":
                    using (SqlDataAdapter sda = new SqlDataAdapter())
                    {
                        sda.SelectCommand = cmd;
                        using (DataTable dt = new DataTable())
                        {
                            sda.Fill(dt);
                            return dt;
                        }
                    }
                case "UPDATE":
                    con.Open();
                    cmd.ExecuteNonQuery();
                    con.Close();
                    break;
            }
            return null;
        }
    }


    protected void Rowdatabound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            SqlCommand cmd = new SqlCommand("select * from Breach_Reason");
            DropDownList ddlbreachreason = (e.Row.FindControl("ddlbreachreason") as DropDownList);
            ddlbreachreason.DataSource = this.ExecuteQuery(cmd, "SELECT");
            ddlbreachreason.DataTextField = "breach_reason";
            ddlbreachreason.DataValueField = "breach_reason";
            ddlbreachreason.DataBind();
            string breach_reason = (e.Row.FindControl("lblbreach") as Label).Text;
            ddlbreachreason.Items.FindByValue(breach_reason).Selected = true;
        }
    }
    protected void oncheckedchanged(object sender, EventArgs e)
    {
        bool isUpdateVisible = false;
        CheckBox chk = (sender as CheckBox);
        if (chk.ID == "Checkall")
        {
            foreach (GridViewRow row in GVData.Rows)
            {
                if (row.RowType == DataControlRowType.DataRow)
                {
                    row.Cells[0].Controls.OfType<CheckBox>().FirstOrDefault().Checked = chk.Checked;
                }
            }
        }
        CheckBox Checkall = (GVData.HeaderRow.FindControl("Checkall") as CheckBox);
        Checkall.Checked = true;
        foreach (GridViewRow row in GVData.Rows)
        {
            if (row.RowType == DataControlRowType.DataRow)
            {
                bool isChecked = row.Cells[0].Controls.OfType<CheckBox>().FirstOrDefault().Checked;
                for (int i = 1; i < row.Cells.Count; i++)
                {
                    row.Cells[i].Controls.OfType<Label>().FirstOrDefault().Visible = !isChecked;
                    if (row.Cells[i].Controls.OfType<TextBox>().ToList().Count > 0)
                    {
                        row.Cells[i].Controls.OfType<TextBox>().FirstOrDefault().Visible = isChecked;
                    }
                    if (row.Cells[i].Controls.OfType<DropDownList>().ToList().Count > 0)
                    {
                        row.Cells[i].Controls.OfType<DropDownList>().FirstOrDefault().Visible = isChecked;
                    }
                    if (isChecked && !isUpdateVisible)
                    {
                        isUpdateVisible = true;
                    }
                    if (!isChecked)
                    {
                        Checkall.Checked = false;
                    }
                }
            }
        }
        Btnupdate.Visible = isUpdateVisible;

    }
    protected void Update(object sender, EventArgs e)
    {
        foreach (GridViewRow row in GVData.Rows)
        {
            if (row.RowType == DataControlRowType.DataRow)
            {
                bool isChecked = row.Cells[0].Controls.OfType<CheckBox>().FirstOrDefault().Checked;
                if (isChecked)
                {
                    SqlCommand cmd = new SqlCommand("update Incident_Details set breach_reason = @breach_reason and Resolution_Cateogarization = @Resolution_Cateogarization where Incident_Number = @Incident_Number");
                    cmd.Parameters.AddWithValue("@Resolution_Cateogarization", row.Cells[2].Controls.OfType<TextBox>().FirstOrDefault().Text);
                    cmd.Parameters.AddWithValue("@breach_reason", row.Cells[3].Controls.OfType<DropDownList>().FirstOrDefault().SelectedItem.Value);
                    
                    this.ExecuteQuery(cmd, "SELECT");
                }
            }
        }
        Btnupdate.Visible = false;
        this.BindGrid();
    }
}