Need help with my recrusive function

[nkad]

I am trying to write a recursive function to return a list of files within folders and subfolders of a given directory.

I get the error, Object reference not set to an instance of an object, when I do FileList.Add.

  Function thisfunction(ByVal path As String, ByVal FileList As ArrayList)
        Dim di As New DirectoryInfo(path)
        Dim folder As DirectoryInfo
        Dim folders() As DirectoryInfo
        Dim file As FileInfo
        Dim files() As FileInfo


        folders = di.GetDirectories()

        For Each folder In folders
            thisfunction(path & "\" & folder.Name, FileList) 
        Next

        files = di.GetFiles

        For Each file In files
            FileList.Add(path & "\" & file.Name) '-capture currentworking path & filename
        Next

    End Function


    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Dim Files As ArrayList

        thisfunction("c:\test", Files)

        MessageBox.Show(Files.Count)
    End Sub