2 функции, 2 таблицы, все одинаково но не работает

Public Function incomebyperod(ByVal startdate As Date, ByVal enddate As Date) As Double
        Dim ttlinc As Double = Nothing
        Dim startdiff As Long = Nothing
        Dim enddiff As Long = Nothing
            For Each incobj As income In incomecollection
                startdiff = DateDiff(DateInterval.Day, incobj.datum, startdate)
                enddiff = DateDiff(DateInterval.Day, incobj.datum, enddate)
                If startdiff <= 0 And enddiff >= 0 Then
 
                    ttlinc += incobj.sum
                End If
            Next
        Return ttlinc
    End Function

Public Function expencebyperiod(ByVal startdate As Date, ByVal enddate As Date) As Double
        Dim expsum As Double
        Dim exstartdiff As Long
        Dim exenddiff As Long
 
        For Each item As expence In expencecollection
            exstartdiff = DateDiff(DateInterval.Day, item.datum, startdate)
            exenddiff = DateDiff(DateInterval.Day, item.datum, enddate)
            If exstartdiff <= 0 And exenddiff >= 0 Then
                expsum += item.sum
            End If
        Next
        Return expsum
    End Function