passing null parameter

[CharChabil]

Private Sub BPrint_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BPrint.Click
Dim frm As New FrmPrintReport 'reports
Dim cr As New CRepResponsable
cr.SetParameterValue(0, Val(Me.TBAccountNumber.Text))'integer
cr.SetParameterValue(1, Me.TBAccountNumber.Text)'string
cr.SetParameterValue(2, vbNull) 'integer
cr.SetParameterValue(3, vbNull) 'string

frm.CrystalReportViewer.ReportSource = cr
frm.MdiParent = Me.MdiParent
frm.Show()
End Sub

i have the code above. i could not pass a null parameter, to the crystal reports. i will have an empty report  i tried vbnull.null and vbnull.empty same result.
but if I put
cr.SetParameterValue(2, Val(Me.TBSubAccount.Text))) 'integer 'not null
cr.SetParameterValue(3, Me.TBSubAccount.Text) 'string 'not null
the report display the values.

here is the select expert formula (CR):

{CUSTOMERS.SUB_ACCOUNT_NUMBER} = {?SubAccount_String} and
{ecole.serial} = {?AccountNumber} and
{CUSTOMERS.ACCOUNT_NUMBER} = {?AccountNumber_String} and
{ecole.sub_account} = {?SubAccount}

How could i pass a null parameter?

[bplacker]

you can't just pass "" as an empty string instead of a null value?

[kenobewan]

Have you tried DBNull.Value?

Hope that this helps.