Using filter to identify if a header is present

I'm struggling trying to find a way to test merely for the existance of
a header entry, in particular, X-UIDL, which currently is only present
in spam mail. It seems like filter cannot do this, at least everything
I've tried doesn't work, using wildcards to match the random string of
digits in the X-UIDL header doesn't do what I want. Is there a way to
test for the mere existance of a header entry, regardless of what it
contains?

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