PLEASE HELP: Visual Basic Error Object reference not set to an instance of an object?

[thefiscster]

I have this visual basic error and i was wondering if anyone could help.

Code:

Private Sub SearchToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SearchToolStripMenuItem.Click



If My.Computer.FileSystem.DirectoryExists("… Then
        If My.Computer.FileSystem.FileExists("conta… Then
             If My.Computer.FileSystem.FileExists("conta… Then
                  Dim a As New System.IO.StreamReader("contacts/list.da…
                  Dim b As New System.IO.StreamReader("contacts/elist.d…

                  Dim c As String = "HOLDER"
                  Dim x As String = "HOLDER"


                Do While Not c = ""
                  c = a.ReadLine
                  x = b.ReadLine
                  If Not c = "" Or x = "" Then
                          Dim search As String = search_t.Text
                          Dim l As Boolean = c.Contains(search)
                          Dim m As Boolean = x.Contains(search)
                          If l = True Or m = True Then
                                  Dim d As New ListViewItem
                                  d.Text = c
                                  d.SubItems.Add(x)
                                  ListView1.Items.Add(d)
                          End If
                  End If


             Loop
               a.Close()
               b.Close()
             End If
       End If
End If
End Sub

I get the Error on this line:

Dim l As Boolean = c.Contains(search)

The error is:
Object reference not set to an instance of an object.

PLEASE HELP! THANK YOU!