The REST sensor raises an error and returns an empty reply if no data is returned from the GET. This then causes an error when evaluating a template sensor.
I currently have this value_template which I think need to change to use state_attr() which I think should avoid an exception being raised.
value_template: "{{ states.sensor.octopus.attributes.results[-1].value_inc_vat|round(2) }}"
How can I do that if the results is an array?
Is there another way of avoiding the error?
Don’t have anything to test now, but have you tried:
value_template: "{{ state_attr('sensor.octopus', 'results')[-1].value_inc_vat|round(2) }}"
Thanks - obvious really, just couldn’t see it.
It passes config check so I’ll see what happens - thanks.
I gave this a shot, but unfortunately it does not have the desired effect. If the restful api call fails, sensors get no data and report erroneously. You can see the effect here: 
I abandoned this approach and wrote a Node-RED node for doing this. There are also a couple of Appdaemon solutions here as well.