How to trigger when last value is not empty

[raulvc]

I wrote a plugin that spits out informative text if there's a backend issue otherwise prints empty ("")
; which is collected through an *item* from a custom template.
I'm trying to create a trigger that: as soon as it detects that the last value isn't empty it screams error (triggering a mail delivery for my team)

I'm struck trying to write the trigger expression, maybe something on the lines of
{template:item[].last() <> empty}=1

any ideas?
Thanks!!