I have two listboxes and one text box. lbxData is already populated with strings (ex; car, boat, motorcycle) I have a text box (tbxRandom) for user input to choose the number of random strings they want generated and placed in the other listbox (lbxRandom) when clicking btnRandom. Here is what I have but keep getting an error. mylist.addrange(str) "value cannot be null. parameter name: collection

Code:
Dim Str As String

        'Declare a List 
        Dim myList As New List(Of String)

        'Mylist gets the values of the existing array
        myList.AddRange(Str)

        'Declare random
        Dim rnd As New System.Random

        'This holds the generated random number
        Dim randomNumber As Integer = 0

        Me.lbxRandom.Items.Clear()


        Dim count As Integer = 0

        'textbox for user to choose the number of randomly generated items
        If Integer.TryParse(tbxRandom.Text, count) Then

            'Keep looping until all items generated
            Do While count <> 0

                'Generate randomNumber 
                randomNumber = rnd.Next(0, myList.Count)

                'Add current item to listbox
                Me.lbxRandom.Items.Add(myList(randomNumber))

                'Remove the used item so it can't be used again
                myList.RemoveAt(randomNumber)

                'Reduce count by 1
                count -= 1
            Loop
        Else
            MessageBox.Show("Problem with that number you entered")
        End If
can anyone tell me what i'm doing wrong