一个查询记录的初级问题

错误提示：未处理的“System.ArgumentNullException”类型的异常出现在 System.Data.dll 中。

其他信息: 值不能为空。
代码如下：各位帮帮忙。如果真能解决再加分。
Imports System.Drawing
Imports System.ComponentModel
Imports System.Windows.Forms
Imports System.Data.OleDb
Imports System.Data
Imports System
Public Class Form3

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        TextBox2.Text = ""
        TextBox3.Text = ""
        TextBox4.Text = ""
        TextBox5.Text = ""
        TextBox6.Text = ""
        TextBox7.Text = ""
        TextBox8.Text = ""
        TextBox9.Text = ""
        TextBox10.Text = ""
        Dim myConn1 As String = " Provider = Microsoft.Jet.OLEDB.4.0 ; Data Source = hyjf.mdb"
        Dim dt As New DataTable
        Dim myConn As OleDbConnection = New OleDbConnection(myConn1)
        myConn.Open()
        Dim str1 As String = " select *  from members " & " where asid= '" & TextBox1.Text & "'"
        Dim cmd As OleDbDataAdapter = New OleDbDataAdapter(str1, myConn)
        Dim myDataSet As DataSet
        cmd.Fill(myDataSet, "members")
        dt = myDataSet.Tables(0)
        TextBox2.Text = dt.Rows(0)("asid").ToString()
        TextBox3.Text = dt.Rows(0)("idcard").ToString()
        TextBox4.Text = dt.Rows(0)("isdate").ToString()
        TextBox5.Text = dt.Rows(0)("name").ToString()
        TextBox6.Text = dt.Rows(0)("fee").ToString()
        TextBox7.Text = dt.Rows(0)("mobil").ToString()
        TextBox8.Text = dt.Rows(0)("ssize").ToString()
        TextBox9.Text = dt.Rows(0)("career").ToString()
        TextBox10.Text = dt.Rows(0)("phy").ToString()
        myConn.Close()
    End Sub
--------------------编程问答-------------------- TextBox3.Text =trim( dt.Rows(0)("idcard").ToString() & "")
--------------------编程问答-------------------- 想到我当年VB期末考试考了19分我就再也不淡定了。

补充：.NET技术 ,  VB.NET