vba:查找最后一行失败,错误91

我使用的代码来自http://ccm.net/faq/14494-vba-last-non-empty-row-all-versions

Function lastRow(sheet As Worksheet) As Long

lastRow = sheet.Columns(1).Find("*", , , , xlByColumns, xlPrevious).Row

End Function

如果工作表包含某些内容,则可以 如果它为空或有内容则失败并显示错误91(对象变量或未设置块变量).

为什么？

考虑:

Function lastRow(sheet As Worksheet) As Variant
   Dim r As Range, lr As Long
   Set r = sheet.Columns(1).Find("*", , , , xlByColumns, xlPrevious)
   If r Is Nothing Then
      lastRow = "Nothing in column"
   Else
      lastRow = r.Row
   End If
End Function