Alertmanager not logging bad request error when posting to v2 api

What did you do?
When I post any json data that is not an array to /v2/api/alerts, alertmanager server doesn't log the bad request error, however, it does when I post it to /v1/api/alerts

e.g.:

$ curl -H "Content-Type: application/json" -d "{}" http://localhost:9093/api/v2/alerts
{"code":400,"message":"parsing alerts body from \"\" failed, because json: cannot unmarshal object into Go value of type models.PostableAlerts"}%

What did you expect to see?
In the alertmanager logs I would expect to see an error. For example for v1 API I would see:

level=error ts=2021-03-31T15:46:14.450Z caller=api.go:780 component=api version=v1 msg="API error" err="bad_data: json: cannot unmarshal object into Go value of type []*types.Alert"

What did you see instead? Under which circumstances?
No logs

Environment

• System information:

$ uname -srn
Linux 47a38d40724b 4.19.121-linuxkit

• Alertmanager version:

$ alertmanager --version
alertmanager, version 0.21.0 (branch: HEAD, revision: 4c6c03ebfe21009c546e4d1e9b92c371d67c021d)
  build user:       root@dee35927357f
  build date:       20200617-08:54:02
  go version:       go1.14.

Reproduce the malformed JSON request against /v2/api/alerts and compare its handling with /v1/api/alerts, using the reported Alertmanager logs as the expected reference. Trace the v2 API request path and identify where the bad request is returned without being logged. Done means malformed non-array JSON returns the existing 400 response and produces an error entry in the Alertmanager logs.