Scrape sensor fallback value

Hi all,

I have a scrape sensor, but the website goes offline time by time (long story). When this happends, the sensor throws an error:

WARNING (MainThread) [homeassistant.components.scrape.sensor] Index '0' not found in sensor.scrape_test

How do I use value_template to counter this effect?
The sensor:


- resource_template: "website"
  scan_interval: 60
  timeout: 60
  sensor:
  - name: "scrape test"
    icon: mdi:airplane
    select: ".value_class"
    index: 0
    value_template: |
      {% if value[0] is none %}
        "unknown"
      {% else %}
        {{ value }}
      {% endif %}

I tried:

{{ value is not none }}
{{ value is defined }}
{{ value is null }}

cheers!