[Zope] catching exceptions in zpt

I'm trying to do something like this in a zpt <meta tal:define="global target python:here.mysript(request.target) | nothing" /> however, if my request did not have ?target=blah I get an attributeError because of course the request has not parameter called target. I assumed that the pipe 'or nothing' would handle an equivalent except AttributeError block but it doesnt. how can I put in my zpt a way to catch if request has no attribute? -- David Bear College of Public Programs/ASU 411 N Central, Phoenix, AZ 85004