Trigger expression question

[messiah]

Hello,

I've stuck on one problem and can't find any solution via search, so...

I wrote this expression in trigger:

{host:system.swap.size[,used].last(0)}>{host:vm.memory.size[total].last(0)}*0.05

But I get this error in server log:

Expression [{13794}>{13793}*0.05] for item [23635][host:system.swap.size[,used]] cannot be evaluated: unable to get function value: lastvalue IS NULL for function [13793][host:vm.memory.size[total].last(0)]

Is it possible to somehow write this expression correctly or it is not possible at all? I don't understand why it doesn't work. I've tried some other variations, but no luck.

[richlv]

item "host:vm.memory.size[total]" has not returned any data since you modified/created the trigger. make/wait for it to do so, and it should work

[messiah]

Thanks a lot for your answer. Seems to be working!