System.Collections.Specialized.NameValueCollection.this[string].get returned null

Question

I have a lender page where I display all the lenders in the database in that I have an option to edit the lenders when I click on the button its showing this error.

System.NullReferenceException: 'Object reference not set to an instance of an object.'

System.Collections.Specialized.NameValueCollection.this[string].get returned null.` 

the code is this

ViewState["lender_id"] = lenderid = Convert.ToInt32(Request.QueryString["lender_id"].ToString());

this is my method I think so

private void Get_lender_data_to_update()
    {
        ViewState["lender_id"] = lenderid = Convert.ToInt32(Request.QueryString["lender_id"].ToString());

        using (dtst = bal.Getlenderedit(lenderid))

        {

            lender_name.Text = dtst.Tables[0].Rows[0]["lender_name"].ToString();
            lender_code.Text = dtst.Tables[0].Rows[0]["lender_code"].ToString();
            //ddlselect.SelectedValue = dtst.Tables[0].Rows[0]["Gender"].ToString();
            manager_name.Text = dtst.Tables[0].Rows[0]["manager_name"].ToString();
            manager_number.Text = dtst.Tables[0].Rows[0]["manager_number"].ToString();
            lc_number.Text = dtst.Tables[0].Rows[0]["lc_number"].ToString();
            manager_email.Text = dtst.Tables[0].Rows[0]["manager_email"].ToString();
            lc_email.Text = dtst.Tables[0].Rows[0]["lc_email"].ToString();
            contact_name.Text = dtst.Tables[0].Rows[0]["contact_name"].ToString();
            designation.Text = dtst.Tables[0].Rows[0]["designation"].ToString();
            branch_name.Text = dtst.Tables[0].Rows[0]["branch_name"].ToString();
            branch_add.Text = dtst.Tables[0].Rows[0]["branch_add"].ToString();
            branch_add2.Text = dtst.Tables[0].Rows[0]["branch_add2"].ToString();
            branch_city.Text = dtst.Tables[0].Rows[0]["branch_city"].ToString();
            branch_state.Text = dtst.Tables[0].Rows[0]["branch_state"].ToString();
            branch_zip.Text = dtst.Tables[0].Rows[0]["branch_zip"].ToString();
            branch_country.Text = dtst.Tables[0].Rows[0]["branch_country"].ToString();


        }

    }

This is my bal.Getlenderedit

public DataSet Getlenderedit(int lenderid)
    {
        return dal.Getlenderedit(lenderid);
    }

This is my dal.Getlenderedit

public DataSet Getlenderedit(int lenderid)
    {
        try
        {
            cmd.Parameters.Clear();
            cmd.Parameters.AddWithValue("@lenderid", lenderid);
            DataSet lenderedit = dbmngr.ExecuteAdapter(cmd, CommandType.StoredProcedure, "editlender");
            return lenderedit;
        }
        catch (Exception ex)
        {

            throw ex;
        }
    }

Answer 1

Thank you @john I have solved this issue

I think this is funny I just removed "_" from these line of code

ViewState["lender_id"] = lenderid = Convert.ToInt32(Request.QueryString["lender_id"].ToString());

changed lender_id to lenderid