VS 2010 Not sure why I'm getting this warning?

Having issues generation my barcode, have a warning "Variable 'str' is used before it has been assigned a value. A null reference exception could result at runtime"


Public Class Form1
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
Close()
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
If (Me.MaskedTextBox1.Text.Length >= 5) Then
Dim strArrays(4) As String
strArrays(0) = Me.digit2bar(Me.MaskedTextBox1.Text.Substring(0, 1))
strArrays(1) = Me.digit2bar(Me.MaskedTextBox1.Text.Substring(1, 1))
strArrays(2) = Me.digit2bar(Me.MaskedTextBox1.Text.Substring(2, 1))
strArrays(3) = Me.digit2bar(Me.MaskedTextBox1.Text.Substring(3, 1))
strArrays(4) = Me.digit2bar(Me.MaskedTextBox1.Text.Substring(4, 1))
Me.TextBox1.Text = String.Concat(strArrays)
Else
Me.TextBox1.Text = "?????????????????????????"
End If
End Sub
Private Function digit2bar(ByVal digit As String) As String
Dim str As String
Dim str1 As String = digit
If (String.Equals(str1, "1", False) <> 0) Then
If (String.Equals(str1, "2", False) <> 0) Then
If (String.Equals(str1, "3", False) <> 0) Then
If (String.Equals(str1, "4", False) <> 0) Then
If (String.Equals(str1, "5", False) <> 0) Then
If (String.Equals(str1, "6", False) <> 0) Then
If (String.Equals(str1, "7", False) <> 0) Then
If (String.Equals(str1, "8", False) <> 0) Then
If (String.Equals(str1, "9", False) <> 0) Then
If (String.Equals(str1, "0", False) <> 0) Then
str1 = "?????"
Else
str = "||..."
End If
Else
str = "|.|.."
End If
Else
str = "|..|."
End If
Else
str = "|...|"
End If
Else
str = ".||.."
End If
Else
str = ".|.|."
End If
Else
str = ".|..|"
End If
Else
str = "..||."
End If
Else
str = "..|.|"
End If
Else
str = "...||"
End If
Val(str)
Return str
End Function
End Class