For the use cases when LLD rule is supposed to always receives a single entity (or none), a better solution would be to cascade the scenario:

1) Execute a 1st check and store received value in cache

2) The monitoring tool will detect when a new value arrives in cache and instantly execute another item. Use received value from the first check as an input for the second check. A second check must be passive, I suppose.

If the first item does not receive a value, the second check is not executed.

Second check can be "Zabbix agent", "SNMP agent", "External check", ..