[RESOLVED] LINQ problem

[Pradeep1210]

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim v1 = (From x In "abcd" Where x = "a" Select x).FirstOrDefault
    Dim v2 = (From x In "abcd" Where x = "m" Select x).FirstOrDefault
    Dim v3 = (From x In "abcd" Where x = "a" Select x).FirstOrDefault
    Dim v4 = (From x In "abcd" Where x = "a" Select x).FirstOrDefault
    Dim result = Nz(v1, "-") & Nz(v2, "-") & Nz(v3, "-") & Nz(v4, "-")
    MsgBox(result)
End Sub

Function Nz(ByVal var As String, ByVal substitiution As String) As String
    Return If(var IsNot Nothing, var, substitiution)
End Function

I was expecting it to produce "a-aa", but the result is "a".
Any ideas why?