Trigger.entity_id empty when triggered by time

1

Anyone solve this one:
I have a automation which can be triggered by a sensor or at specific times. If I try to report which triggered it I get blank if time triggered it. BUT I can’t work out how to script the test for blank.

  trigger:
    - platform: state
      entity_id: binary_sensor.curtain_not_needed
      to: "on"
    - platform: sun
      event: sunset
      offset: "-00:30:00"
    - platform: time
      at: "08:30:00"
  action:
    - service: notify.pushover
      data_template:
        message: >
          Opening curtains. Triggered by {% if trigger.entity_id != '' %} '{{trigger.entity_id}}' {%else%} Time: {{now().time}} {%endif%}

The test == ‘’ fails to match a blank entity_id, I’ve also tried == none.

Any suggestions?