Ошибка: Error: System.Data: ExecuteReader: CommandText property has not been initialize

Imports System.Data.SqlTypes
 
'Public Class Form1
Public Class Form1
    Inherits System.Windows.Forms.Form
 
    Dim mda As New SqlClient.SqlDataAdapter()
    Dim mds As New DataSet()
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
 
    End Sub
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim cnn As New SqlClient.SqlConnection()
        Dim cmd As New SqlClient.SqlCommand()
        Dim da As New SqlClient.SqlDataAdapter()
        Dim ds As New DataSet()
        Dim cmdUpdate As New SqlClient.SqlCommand
        Try
                      
            cnn.ConnectionString = "Data Source=СЕРГЕЙ-ПК\SQLEXPRESS;Initial Catalog=dddd;Integrated Security=True"
            cnn.Open()
            cmd = cnn.CreateCommand
            da.SelectCommand = cmd
            da.Fill(ds, "work")
            cnn.Close()
            dgMain.DataSource = ds
            dgMain.DataMember = "work"
 
            MsgBox("Связь прошла!!!!!")
 
        Catch ex As Exception
            MsgBox("Error: " & ex.Source & ": " & ex.Message, MsgBoxStyle.OkOnly, "button4")
        End Try
 
    End Sub
 
   End Class