主题：临时表，运行时报错

制作临时表，运行时报错

从字符串“”到类型“Double”的转换无效。

老师帮我看看这段码的问题

For Each dc As Col In t1.Cols
    For Each dr As Row In t1.Rows
        flt = "类号 = '" & dr("类号") & "' and 材料名称 = '" & dr("材料名称") & "' and 出生日期  = '" & dr("出生日期") & "'"
        Select Case dc.name
            Case "材料最早形成时间"
                exp = "Min(" & dic(dr("审核内容")) & ")"
                dr(dc.name) =dt.Compute(exp,flt)
            Case "材料最新形成时间"
                exp = "Max(" & dic(dr("审核内容")) & ")"
                dr(dc.name) =dt.Compute(exp,flt)
        End Select
    Next
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