Null refernce exception during serial port communication attempt

Dim withevents COMPort as SerialPort
Dim comOpen as Boolean

Private Sub Form1_FormClosed(ByVal sender as object, ByVal e As System.Windows.Forms.FormCLosedEventArgs)Handles Me.FormClosed

With COMPort 
    .POrtName = "COM20"
    various other properties

End with

If COMPort.IsOpen then
   COMPort.Colse()
End If
End Sub

Private Sub Form1_Load(ByVal sender as  system.object, ByVal e As System.EventArgs)Handles MyBAse.Load
Dim Portnames as string() = serialPort.GetPortNames
if Portnames is nothing then 
MsgBox ("None detected")
Me.Close()
End IF

cbComPort.Items.AddRange(Portnames)
cbComPort.Text = Portnames(0)
End Sub

Private sub btnConnect_Click(ByVal Sender As System.Object, byval e as System.EventArgs) handles btnConnect.Click

Try
 COMPort.Open()
 comOpen = ComPort.IsOpen
Catch
 comOpen = False
 MsgBox("Error Open: " & ex.Message)
End Try

If COMport.IsOPen Then  ' ERROE HERE null reference exception
 COMPort.Write("01")

End If
End Sub


Dim readBuffer as string

Private Sub COMPort_DataReceived(ByVal sender as system.Object, ByVal e As SerialDataReceivedEventArgs) HAndles COMPort.DataReceived

Try
    readBuffer  = COMPort.ReadLine()
    Me.Invoke(New EventHandler(AddressOf DoUpdate))
Catch
  MsgBox("read " &ex.Message)
End Try
End Sub

Public Sub DoUpdate(ByVal sender as Object, Byval e as System.EventArgs)

tbRx.text = readBuffer

End Sub

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