[Twisted-web] How to render an empty stan tag in Nevow

Hello, I have a situation like this: class myPage(rend.Page): def render_salute(self, context, data): rv = if <condition>: rv = loaders.stan(T.p['You made it']) return rv docFactory = loaders.stan( .... T.invisible(render=T.directive('salute')) .... What I want in render_salute is to return 'nothing' if <condition> is false. Basically, as if the T.invisible in the docFactory didn't exist. I've tried = loaders.stan(T.p['']) but it has the side effect of forcing a line break which is undesirable (in my real code the T.invisible is inside a table cell). Even returning a   string would do it! Any suggestions? Thanks, -- Pedro