How to fix this "null reference" error message?

This is some code from Microsoft's VB .NET samples.
The error message is:
Variable 'ts' is used before it has been assigned a value. A null reference exception could result at runtime.

How to fix it?

......
Dim ts As StreamReader
 
	     Try
		    With odlgTextFile
                                .CheckFileExists = True
                    ......
				If .ShowDialog() = DialogResult.OK Then
					FileName = .FileName
					ts = New StreamReader(.OpenFile)
					txtFileContents.Text = ts.ReadToEnd()
				End If
			End With
		Catch exp As Exception
			MessageBox.Show(exp.Message, Me.Text)
        Finally
            If Not (ts Is Nothing) Then
                ts.Close()
            End If
		End Try

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