Null Reference Exception when trying to upload a file via FTP - vb.net

Question

I made a FTP upload application, which changes the name of the file chosen in FileDialog to a set of variables from 4 ComboBoxes. But whenever i try to upload the file it says:
Path Cannot be Null Paramenter name: path
in the immediate window it says:
A first chance exception of type 'System.ArgumentNullException' occurred in mscorlib.dll
A first chance exception of type 'System.NullReferenceException' occurred in Microsoft.VisualBasic.dll
and this:
i've gone over the code multiple times but i do not understand what is wrong, since i am quite new to VB.
this is the code i used:
Dim Filename As String
Dim originalFile As String
Private Function enumerateCheckboxes(ByVal path As String)
originalFile = path
Dim fName As String
For Each Control In Me.Controls
If (TypeOf Control Is ComboBox AndAlso DirectCast(Control, ComboBox).SelectedIndex > -1) Then
fName += CStr(Control.SelectedItem.Key) + "_"
End If
Next
Try
fName = path + fName.Substring(0, fName.Length - 1) + ".pdf"
Catch ex As Exception
MsgBox(ex.Message)
MsgBox("Stack Trace: " & vbCrLf & ex.StackTrace)
End Try
Return fName
End Function
Public Function OpenDialog()
Dim FD As OpenFileDialog = New OpenFileDialog()
FD.Title = "Selecteer een bestand"
FD.InitialDirectory = "C:\"
FD.Filter = "All files (*.*)|*.*|All files (*.*)|*.*"
FD.FilterIndex = 2
FD.RestoreDirectory = True
If FD.ShowDialog() = DialogResult.OK Then
Dim Filename As String = FD.FileName
Filename = StrReverse(Filename)
Filename = Mid(Filename, InStr(Filename, "\"), Len(Filename))
Filename = StrReverse(Filename)
MsgBox(enumerateCheckboxes(Filename))
End If
End Function
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim request As System.Net.FtpWebRequest = DirectCast(System.Net.WebRequest.Create("ip"), System.Net.FtpWebRequest)
request.Credentials = New System.Net.NetworkCredential("username", "password")
request.Method = System.Net.WebRequestMethods.Ftp.UploadFile
Dim file() As Byte
Try
Filename = OpenDialog()
System.IO.File.ReadAllBytes(Filename)
Catch ex As Exception
MessageBox.Show(ex.Message)
MessageBox.Show("Stack Trace: " & vbCrLf & ex.StackTrace)
End Try
FileSystem.Rename(originalFile, Filename)
Dim strz As System.IO.Stream = request.GetRequestStream()
strz.Write(file, 0, file.Length)
strz.Close()
strz.Dispose()
FileSystem.Rename(Filename, originalFile)
End Sub
Thank you in advance

Answer 1

An ArgumentNullException is not a NullReferenceException. It's telling you the argument to one of the functions is Nothing.
It's being caused in part by these two lines:
Filename = OpenDialog()
System.IO.File.ReadAllBytes(Filename)
In this case, it appears that your Filename is Nothing, because OpenDialog doesn't return a value. You'll need to return the file selected from the OpenFileDialog.