VB - Doppelte Einträge löschen

Public Class Form1

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim OldList As New List(Of String)
        Dim NewList As New List(Of String)


        OldList.Add("aaaa".ToString)
        OldList.Add("aaaa".ToString)
        OldList.Add("cccc".ToString)
        OldList.Add("aaaa".ToString)
        OldList.Add("bbbb".ToString)
        OldList.Add("aaaa".ToString)


        NewList = DelDblEntr(OldList)
        ListBox1.Items.AddRange(NewList.ToArray)

    End Sub


Private Function DelDblEntr(ByVal RntyList As List(Of String)) As List(Of String)
        DelDblEntr = Nothing

        DelDblEntr = RntyList.Distinct().ToList()

End Function