How to find mails which are sent to 'undisclosed-recipients' ?

[Vladimir Marek]

Hi,

Since my mail works in a way that it hides everything but what I
selected to be shown to me, I was overlooking all mails which where sent
to undisclosed-recipients. I tried to match such mails by
to:undisclosed-recipients but that does not seem to work. Is there any
workaround to find such mails?

Thank you
-- 
        Vlad