Try creating an agent with below code and run it via web (e.g. from action button on a web form) so that it runs on server. You will be really surprised - your server will stop working.At first it looks only http process is down, but it will crash all the stuff. It is tested 
Sub Initialize
On Error Goto ummm
Dim a As Variant
Redim a(0)
a = ":-)"
a = Arrayappend (a,getnull())
Exit Sub
ummm: Print(“So we are here…”)
Exit Sub
End Sub
Function getnull() As Variant
getnull = Null
End Function
Conclusion: never use unhandled function call as a parameter in arrayappend function.
Instead
a = Arrayappend (a,getnull())
rather use
b = getnull()
a = Arrayappend (a,b)
and it will run without any complaint…
Nice bug, isn’t it ?