[Zope] <dtml-var x missing> doesn't work?

[Chris Withers]

Hi,

I'm doing a back link to go on a page (yes, I know browsers have back buttons, but some people don't
like to use them ;-) which is easy enough:

<A href="<dtml-var "REQUEST.environ['HTTP_REFERER']">">Back</A>

except that if there is no referer, you get a key error. So I thought I'd try the following:

<A href="<dtml-var "REQUEST.environ['HTTP_REFERER']" missing='/'>">Back</A>

But I still get a key error. I thought the 'missing' attribute was supposed to catch that?

Chris