leak-detector-notifier.yaml

blueprint:
  name: Leak detection & notifier
  description: Send a notification when any configured moisture sensor becomes moist
  domain: automation
  input:
    notify_device:
      name: Notify device
      description: "The device where the notification should be sent to."
      selector:
        device:
          integration: mobile_app

trigger:
  - event_data: {}
    event_type: state_changed
    platform: event

condition:
  - condition: template
    value_template: '{{ trigger.event.data.new_state.attributes.device_class == "moisture" }}'
  - condition: template
    value_template: '{{ trigger.event.data.new_state.state == "on" }}'

action:
  domain: mobile_app
  type: notify
  device_id: !input notify_device
  message: "{{ trigger.event.data.new_state.attributes.friendly_name }} has detected a leak."
  title: "Leak detected!"

mode: single

Getting an error recently: Template variable error: 'None' has no attribute 'attributes'
when rendering '{{ trigger.event.data.new_state.attributes.device_class == "moisture" }}'

chatgpt tells me:
The error 'None' has no attribute 'attributes' happens when trigger.event.data.new_state is None. This can happen if a sensor is deleted, unavailable, or for some reason the event doesn’t include a new_state.

In Home Assistant, a safe way to handle this is to check that new_state exists before accessing its attributes. You can change your condition to:

and proposes this fix

- condition: template value_template: > {% if trigger.event.data.new_state %} {{ trigger.event.data.new_state.attributes.device_class == 'moisture' }} {% else %} false {% endif %}