主题：[求助]导出数据

 帮助文件————导出数据
下面代码，当日期列单元格为空时，导出的excle表的单元格 日期是1900-01-00，下面代码怎么修改呢？谢谢

Dim dt As Table = Tables("订单")
Dim nms() As String = {"产品","客户","数量","单价","金额","日期"} '要导出的列名
Dim caps() As String = {"产品名称","用户名称","数量","单价","金额","日期"} '对应的列标题
Dim szs() As Integer = {100,100,80,80,80,120} '对应的列宽
Dim Book As New XLS.Book '定义一个Excel工作簿
Dim Sheet As XLS.Sheet = Book.Sheets(0) '引用工作簿的第一个工作表
Dim st As XLS.Style = Book.NewStyle '日期列的显示格式
st.Format = "yyyy-MM-dd"
For c As Integer = 0 To nms.length -1
    Sheet(0, c).Value = caps(c) '指定列标题
    Sheet.Cols(c).Width = szs(c) '指定列宽
    If dt.Cols(nms(c)).IsDate Then '如果是日期列
        Sheet.Cols(c).Style = st '设置显示格式
    End If
Next
For r As Integer = 0 To dt.Rows.Count - 1 '填入数据
    For c As Integer = 0 To nms.length -1
        Sheet(r +1, c).Value = dt.rows(r)(nms(c))
    Next
Next
Dim dlg As New SaveFileDialog '定义一个新的SaveFileDialog
dlg.Filter= "Excel文件|*.xls" '设置筛选器
If dlg.ShowDialog = DialogResult.Ok Then
    Book.Save(dlg.FileName)
    Dim Proc As New Process
    Proc.File = dlg.FileName
    Proc.Start()
End If