I have a VB.NET application with reports (using Microsoft Reportviewer).

I have searched, but cannot find a answer to my problem.

I want to show all records on the report if the reportparameter is null. I use a combobox to choose the report parameter name.


Code:
Dim stringaliasnaam As String


        If KiesVorm.CmbAliasnaam3.SelectedIndex <> -1 Then
            stringaliasnaam = KiesVorm.CmbAliasnaam3.SelectedItem.ToString
        Else
            stringaliasnaam = Nothing

        End If


        Dim param1 As New ReportParameter("ReportParameterAliasnaam", stringaliasnaam)


        Me.ReportViewer1.LocalReport.SetParameters(New ReportParameter() {param1})

        ReportViewer1.Show()
        Me.ReportViewer1.RefreshReport()

I set the reportparameter properties to Allow Null.
In a tablix properties I set the Filter to = isnothing(Parameters!ReportParameterAliasnaam.Value)
I make the type Boolean. I use = as the operator and the value as =false


When I run the application, I get no error messages, but the results in the report are wrong. If I select something from the combobox all records are displayed and when I select nothing the report is empty.

I want the report to display the records for the selection in the combobox and if nothing is selected I want to see all records.

Can someone please let me know what I am doing wrong ?