How can I extract some events from iCal ?

Hi All,
I have a calendar with some events.
Some of them have the url field empty e others have the url field not empty.

I have to extract ONLY events with url field empty and I tried the following 4 solution but nothing:

tell application “iCal”

set MyCalendar to (the first calendar whose title is “MyPersCal”)

set EventRef to (first event of MyCalendar whose url is none)
set EventRef to (first event of MyCalendar whose url is “”)
set EventRef to (first event of MyCalendar whose url is empty)
set EventRef to (first event of MyCalendar whose url is null)

end tell

These 4 solutions does not work at all!!

What is the exact syntax to catch those kind of events of url empty ?

Thanks

Gianni

here is a quick an dirty one that i came up with in 2min but it will get your events your after, just might take a while took 10sec on my laptop.

tell application "iCal"
	set myEvents to properties of every event of every calendar
	set myList to {}
	repeat with theCal in myEvents
		repeat with theEvent in theCal
			if url of theEvent is missing value then
				set myList to myList & theEvent
			end if
		end repeat
	end repeat
end tell
myList