I am trying to insert a record in sql database using vb.net dataadapter, datatable, and datarow features. I use the following code but it gives me an error:

Object reference not set to an instance of an object

Imports System.Data.SqlClient
Public Class Form1  
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim cn As New SqlConnection("Data Source=.\SQLEXPRESS;Initial Catalog=drpractice;Integrated Security=True")
        Dim da As New SqlDataAdapter
        Dim ds As New DataSet

        Try
            cn.Open()
            da.SelectCommand = New SqlCommand("SELECT * FROM [emp_tbl]", cn)
            da.Fill(ds) 
            Dim dt As New DataTable
            dt = ds.Tables("emp_tbl")

            'Error in this line(Object reference not set to an  instance of an object)'
            Dim dr As DataRow = dt.NewRow() 

            dr.Item("emp_id") = TextBox1.Text.Trim
            dr.Item("emp_name") = TextBox2.Text.Trim
            dr.Item("salary") = TextBox3.Text.Trim
            dr.Item("age") = TextBox4.Text.Trim
            dr.Item("emp_group") = TextBox5.Text.Trim
            dt.Rows.Add(dr)
            da.Update(ds)
            MsgBox("Record Successfully Inserted")
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub
End Class