主题：代码运行出错

.NET Framework 版本：2.0.50727.3649
Foxtable 版本：2013.10.14.1
错误所在事件：表，试样台账， DataColChanged
详细错误信息：
Exception has been thrown by the target of an invocation.
Conversion from string "" to type 'Integer' is not valid.
Input string was not in a correct format.

在表属性运行代码：

If e.DataCol.name = "编号"
    If e.DataRow("编号").Contains("-") Then
       Dim vs As String() = e.DataRow("编号").split("-")
       e.DataRow("编号") =  format(Val(vs(0)),"0000") & "-" & vs(1)
    Else
        Dim v As Integer = e.DataRow("编号")
        e.DataRow("编号") =  format(v ,"0000")
    End If
End If

保存时报错，麻烦老师帮忙看看