Help with trigger expression in zabbix?

Question

linux

Good afternoon.
There is a trigger in zabbix with the following expression:
{Template SNMP Junger:temperature.last()}=2
What does it mean if the temperature on the device = 2 (the value received via the snmp protocol) notify the network administrator about this.
Question: How to modify the trigger if it has not received any value. Usually, if you have not received any knowledge, it shows "-"
What you need to replace 2 in order to achieve the goal
Question two.
There is an audio encoder in which network cards are constantly added and removed.
There is an OID for counting network cards in the device.
At the moment there are 8 of them. I would like that if the number changes to 9 (etc) , the trigger notifies that the number of cards has changed.
I think it should be something like
{Device.modulesNumber.min(1) <> Device.modulesNumber.last() - notify about events. In this case, after a minute, the trigger should go away on its own. But it doesn't work

Answer 1

RESOLVED.
To solve the first question, use the following expression
{Device:temperature.nodata(360)}
To solve the second question:
{Device.modulesNumber.last()} < {Device.modulesNumber.prev()}