Template warning: `history_event_list_1_datetime` missing from `state_all` payload when aggregate has no data

[linky67]

Hello,

I'm running the Docker image and using Home Assistant 2026.8.1. Home Assistant repeatedly logs the following warning:

Logger: homeassistant.helpers.template
Source: helpers/template/__init__.py:685
Template variable warning: 'dict object' has no attribute 'history_event_list_1_datetime' when rendering '{{ value_json.history_event_list_1_datetime }}'

This occurred 400 times over ~26 minutes, so it's firing on (or near) every MQTT publish cycle.

Cause (as far as I can tell from SOFAR-HYD-3PH-AND-G3.json):

history_event_list_1 is a "normal" register (read directly at 0x1480), but history_event_list_1_datetime has no register field — it's computed via aggregate_datetime_bitmap from three separate registers (year_month 0x1481, day_hour 0x1482, minute_second 0x1483):

{
  "name": "history_event_list_1_datetime",
  "aggregate_datetime_bitmap": {
    "year_month": "0x1481",
    "day_hour": "0x1482",
    "minute_second": "0x1483"
  },
  "ha": {
    "name": "History Event List 1 - DateTime",
    "value_template": "{{ value_json.history_event_list_1_datetime }}"
  }
}

It looks like this computed key isn't always included in the sofar/state_all JSON payload — possibly only when the aggregation produces a non-empty/valid result. Since the HA auto-discovery config points value_template directly at value_json.history_event_list_1_datetime with no fallback, HA logs a warning every time the key is absent from the payload.

Suggested fix:

Either:

1. Always include history_event_list_1_datetime in state_all (e.g. null/empty string when the aggregate has no valid data yet), so the key is consistently present, or
2. Add a default to the generated value_template, e.g. {{ value_json.history_event_list_1_datetime | default('') }}, so HA doesn't warn when the key is briefly absent.

Happy to test a fix if useful — thanks for the great project!