https://www.zabbix.com/documentation/2.4/manual/config/triggers/expression#examples_of_triggers

In example 8 is mistake: "'tick' must have type 'Zabbix trapper'. "

From IRC:
"
[15:06] <Richlv> saying that it must be trapper does look like something quite old & wrong by now
[15:07] <Richlv> or maybe it tries to have a very specific example, but ends up confusing
[15:07] <Richlv> it should be rewritten indeed. wiuempe please report a new bug
"