How can exception have a NullReferenceException [duplicate] - asp.net

Question

This question already has answers here:
What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 5 years ago.
My code updates & inserts into a bunch of tables. About 2 months ago I got the same error as the one below, I assumed it was because the exception it self is Nothing.
So I built in a test to check if it isn't nothing, write the exception details.
However, the error in the screenshot occurred again this morning. My question now is how does a code block like the one below result in the Exception being Null, and in which cases will an exception be Null?
Edited - This is different to this question because I want to know how an EXCEPTION can be Null/Nothing
Try
If t.DpaPosted = "N" Then
i += 1
OutputCount += 1
Dim SubAccountID As Integer = 0
If t.SubaccountId = 0 Then
SubAccountID = GetSubAccountID(t.DpaInId)
If SubAccountID = 0 Then
If DupAcc > 1 Then
UpdateLog(t.clientReference & " - Multiple CLOSED(Paid Up/Refunds outstanding) accounts.")
Else
SubAccountID = GetClosedSubAccountID(t.DpaInID)
If SubAccountID = 0 Then
UpdateLog(t.clientReference & " - No accounts found.")
End If
End If
End If
End If
If SubAccountID <> 0 Then
If t.DpaDocNo <> "0" Then
If q.Execquery("SELECT COUNT(1) FROM Transactions WHERE SubAccountID = " & t.SubaccountId & " AND TranTypeID = 6 AND TranAmount = " & t.DpaAmount & " AND DPANo = '" & t.DpaDocNo & "'") > 0 Then
HttpContext.Current.Response.Write("Sequence [" & t.DpaDocNo & "] already posted.<br/>")
dpaadapter.SetDpaPosted(t.DpaInId)
Else
PostDpa(SubAccountID, 6, t.DpaAmount, t.Dpadate, "0", t.DpaDocNo)
dpaadapter.SetDpaPosted(t.DpaInId)
End If
Else
PostDpa(SubAccountID, 6, t.DpaAmount, t.Dpadate, "0", t.DpaDocNo)
dpaadapter.SetDpaPosted(t.DpaInId)
End If
End If
If WriteOutput Then HttpContext.Current.Response.Write("Imported [" + i.ToString + "] of [" + dpa.Rows.Count.ToString + "]<br/>")
If OutputCount = 10 Then
OutputCount = 0
If WriteOutput Then
If HttpContext.Current.Response.IsClientConnected Then
HttpContext.Current.Response.Flush()
HttpContext.Current.Response.Write("<script>window.scrollTo(0,document.body.scrollHeight);</script>")
HttpContext.Current.Response.Flush()
End If
End If
End If
End If
Catch ex As Exception
Dim LogStr As String = ""
LogStr = "Record [" & i.ToString & "]. "
LogStr = "Ref [" & t.clientReference & "] - "
If ex.Message.ToString <> Nothing Then LogStr = LogStr & ex.Message.ToString Else LogStr = LogStr & "No Exception Message"
If ex.InnerException.ToString <> Nothing Then LogStr = LogStr & vbCrLf & ex.InnerException.ToString Else LogStr = LogStr & "No Inner Exception"
UpdateLog(LogStr)
SaveLog()
End Try
I can't actually see what code is triggering the exception, until I can fix the exception handling.
Some more information that might help
I am using asp.net V 4.0
The code is in a class, and the file is located in the appcode directory.
The issue doesn't always trigger
When running the code for a second/third time, the exception doesn't trigger again. So I can't recreate the error all the time.
Windows event viewer didn't log any exceptions for this page.
ANSWER
Found from this question.
An inner exception is the exception that caused the current exception.
It is used in cases when you want to surface a different exception
than the one that your code caught but you don't want to throw away
the original context.
In order for a new exception to have information about a previous one,
like you said, you pass it as constructor parameter to the new one.
Usually, a null inner exception means that the current exception is
root cause of the exceptional situation.

Answer 1

How about safeguarding your ex.InnerException? Once you make sure that an InnerException exists then you can access its methods and properties.
If ex.InnerException Is Not Nothing AndAlso ... Then
See this explanation (and read the accepted answer) about InnerException. It is not necessary to have an InnerException, unless the current exception was caused by another exception.