"Object cannot be cast from DBNull to other types."

Question

Response<BranchDeleteResponse> response = new Response<BranchDeleteResponse>();

// calling Deletion API
response = new ApiManager().InvokeGetHttpClientWithoutRequest<Response<BranchDeleteResponse>>(Baseurl + "api/BranchDelete").Item1;

if (Convert.ToString(response.status) == "SUCCESS" && response.Data.isDataAvailable)
{
    Response<BranchMasterResponse> response2 = new Response<BranchMasterResponse>();

    string str = "select * from branch_master";
    dtaccount = dbobj.GetDataTable(str, null, CommandType.Text);
               
    List<BranchInsertRequestData> brlist = new List<BranchInsertRequestData>();
                
    if (dtaccount.Rows.Count > 0)
    {
        for (int i = 0; i <= dtaccount.Rows.Count - 1; i++)
        {
            // AccountInsertReq accountRequest = new AccountInsertReq();
            BranchInsertRequestData branch_request = new BranchInsertRequestData();
                     
            branch_request.BRANCH_ID = Convert.ToInt32(dtaccount.Rows[i][0]);
            branch_request.BRANCH_NAME = Convert.ToString(dtaccount.Rows[i][1]);
            branch_request.FIRM_ID = Convert.ToInt32(dtaccount.Rows[i][2]);
            branch_request.REGION_ID = Convert.ToInt32(dtaccount.Rows[i][3]);
            branch_request.DISTRICT_ID = Convert.ToInt32(dtaccount.Rows[i][4]);
            branch_request.STATE_ID = Convert.ToInt32(dtaccount.Rows[i][5]);
            branch_request.TRA_DT = Convert.ToDateTime(dtaccount.Rows[i][6]);
            branch_request.UPTO_DATE = Convert.ToChar(dtaccount.Rows[i][7]);
            branch_request.STATUS_ID = Convert.ToInt16(dtaccount.Rows[i][8]);
            branch_request.INAUGURATION_DT = Convert.ToDateTime(dtaccount.Rows[i][9]);
            branch_request.BRANCH_NO = Convert.ToInt32(dtaccount.Rows[i][10]);
            branch_request.INT_WAIVER_APPRD = Convert.ToInt16(dtaccount.Rows[i][11]);
            branch_request.SHIFT_ID = Convert.ToInt32(dtaccount.Rows[i][12]);

            brlist.Add(branch_request);
        }

        BranchMasterRequest br_insertreq = new BranchMasterRequest();
        br_insertreq.branch_InsertReq_Datas = brlist;
    }
}

When control goes to loop at

branch_request.FIRM_ID = Convert.ToInt32(dtaccount.Rows[i][2])

an exception is thrown:

Object cannot be cast from DBNull to other types