Alerts do not include "endsAt"

Grafana Alerting
1

I have configured an external alertmanager but the alerts are resolved after a default time as alertmanager requires an “endsAt” to be in the payload.

  # ResolveTimeout is the default value used by alertmanager if the alert does
  # not include EndsAt, after this time passes it can declare the alert as resolved if it has not been updated.
  # This has no impact on alerts from Prometheus, as they always include EndsAt.
  [ resolve_timeout: <duration> | default = 5m ]

How do I ensure endsAt is sent in the alerts?

2

I now see that the value being sent is 0001-01-01 00:00:00 +0000 UTC when an alert is not resolved.

endsAt	string	End time of the alert, default value when not resolved is 0001-01-01T00:00:00Z

but alertmanager handles endsAt like so

endsAt is only set if the end time of an alert is known