Problem about LINQ?

[fairymemay (noona)]

I use code as below.

DT_Detail.AsEnumerable().Where(Function(w) CInt(w("PAID_DATE")) >= [ValueToCompareWith] And CInt(w("PAID_DATE")) <= [ValueToCompareWith2]).CopyToDataTable

But now error as below.
Assign: Conversion from string “” to type ‘Integer’ is not valid.

How to solve it ? ( some row have blank data)