Check Empty/ Null value in the Data Table and replace null values with custom value

Below i have used a gridview and putted some data inside gridview containing few null values inside data columns and replacing all null values with string "Data Not Avaialable" ::

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

public partial class ValueAgainstNull : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            BindData();
        }
    }
    protected void BindData()
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("UserId", typeof(Int32));
        dt.Columns.Add("Name", typeof(string));
        dt.Columns.Add("Designation", typeof(string));
        dt.Columns.Add("Department", typeof(string));

        DataRow dr = dt.NewRow();
        dr["UserId"] = 1;
        dr["Name"]="Aayush";
        dr["Designation"] = "Associate Technical Consultant";
        dr["Department"] = null;
        dt.Rows.Add(dr);

        dr = dt.NewRow();
        dr["UserId"] = 2;
        dr["Name"] = "Anish";
        dr["Designation"] = null;
        dr["Department"] = null;
        dt.Rows.Add(dr);

        dr = dt.NewRow();
        dr["UserId"] = 3;
        dr["Name"] = "Manish";
        dr["Designation"] = null;
        dr["Department"] = "Navision";
        dt.Rows.Add(dr);

        dr = dt.NewRow();
        dr["UserId"] = 4;
        dr["Name"] = "Ravish";
        dr["Designation"] = "Tech Lead";
        dr["Department"] = "CRM";
        dt.Rows.Add(dr);

        for (int i = 0; i < dt.Rows.Count; i++)
        {
            for (int j = 0; j < dt.Columns.Count; j++)
            {
                if (string.IsNullOrEmpty(dt.Rows[i][j].ToString()))
                {
                    dt.Rows[i][j] = "Data Not Available";
                }
            }
        }
        gvDetails.DataSource = dt;
        gvDetails.DataBind();
    }
}

Above code behind part would be used to bind the few sample records with gridview control.