งงมากครับ ตอนนี้ผม เป็น Conversion from type 'DBNull' to type 'String' is not valid "ดังรูป" ในการรับจาก DB

 Dim use As String
        Dim passs As String
        use = Class1.uss
        passs = Class1.pass

     

        Dim connectionString As String = "Server=PONGWICS2014-PC;UID=" & use & ";PASSWORD=" & passs & ";Database=Top_CustomerEntry;Connect Timeout=200; pooling='true'; Max Pool Size=200"
        Dim ds As New DataSet


        Dim connection As New SqlConnection(connectionString)




        Dim sql As String = "SELECT AreaID,Area,Team,ZuelligArea FROM AreaMaster  Where  AreaID = '" & ComboBox1.Text & "'"
     


      
          




        If IsDBNull(ds.Tables("AreaMaster").Row(i)("txtteam.Text")) Then

            Name = ""

        Else

            Name = ds.Tables("AreaMaster").Row(i)("txtteam.Text")

        End If
        ComboBox1.ValueMember = "Area"
        ComboBox1.DisplayMember = "AreaID"
        txtarea.Text = ComboBox1.SelectedValue




            Me.txtarea.Text = sTable.Rows(0)("Area")

            Me.txtteam.Text = sTable.Rows(0)("Team")

            Me.txtzuellig.Text = sTable.Rows(0)("ZuelligArea")





    'ComboBox1.ValueMember = "Team"
    'ComboBox1.DisplayMember = "AreaID"
    'txtteam.Text = ComboBox1.SelectedValue



    'ComboBox1.ValueMember = "ZuelligArea"
    'ComboBox1.DisplayMember = "AreaID"
    ' txtzuellig.Text = ComboBox1.SelectedValue


    'End If
    'sDs = New DataSet()
        ComboBox1.Refresh()
    'sAdapter.Fill(sDs, "AreaID")

    'sTable = sDs.Tables("Area")

    
   
        SerachGrid("select * from  AreaMaster where AreaID like '%" & ComboBox1.Text & "%'")

        connection.Close()