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如图：excel里的日期列是字符型，系统里是日期型的，因为有空值导入不了，我将列转换成日期型，空值也不能导入

求助：在导入系统前判断U列是否为空值，如果是空的话赋予一个初始值，代码怎么写

参考下面的代码

Dim dlg As new OpenFileDialog
dlg.Filter = "EXCEL文件|*.xls;*.xlsx"
If dlg.ShowDialog = DialogResult.OK Then
    Tables("TempX").StopRedraw
    Dim Book As New XLS.Book(dlg.FileName)
    Dim Sheet As XLS.Sheet = Book.Sheets(0)
    Dim nms() As String = { "RegDate","Title","V" }    \'这里RegDate是日期列,另外两个分别是字符串和数字
    For i As Integer = 1 To Sheet.Rows.Count -1
        Dim r As DataRow = DataTables("TempX").AddNew()
        For m As Integer = 0 To nms.Length - 1
            If DataTables("TempX").DataCols(nms(m)).IsDate Then
                r(nms(m)) = Cdate(Sheet(i,m).Value)
            ElseIf DataTables("TempX").DataCols(nms(m)).IsNumeric
                r(nms(m)) = val(Sheet(i,m).Value)
            Else
                r(nms(m)) = Sheet(i,m).Value
            End If
        Next
    Next
    Tables("TempX").ResumeRedraw
End If