Filebeat GeoIP not working with dotted field

[Bryserker]

I'm trying to ingest Windows IIS logs with the Filebeat IIS module.

The pipeline that Filebeat has automatically defined for this includes GeoIP lookups, e.g.:

  "geoip" : {
      "field" : "source.ip",
      "target_field" : "source.geo",
      "ignore_missing" : true
  }

However, I noticed the geo fields were never present.

I recreated this manually by following the guide here:

https://www.elastic.co/guide/en/beats/filebeat/7.7/filebeat-geoip.html

First I created the pipeline:

PUT _ingest/pipeline/geoip-info
{
  "description": "Add geoip info",
  "processors": [
    {
      "geoip": {
        "field": "source.ip"
      }
    }
  ]
}

Then I tried ingesting a document through the pipeline:

PUT geoip-test2/_doc/my_id?pipeline=geoip-info
{
  "source.ip": "8.8.8.8"
}

This gives the following output:

{
  "error" : {
    "root_cause" : [
      {
        "type" : "illegal_argument_exception",
        "reason" : "field [source] not present as part of path [source.ip]"
      }
    ],
    "type" : "illegal_argument_exception",
    "reason" : "field [source] not present as part of path [source.ip]"
  },
  "status" : 400
}

It does work if I manually change it to:

PUT geoip-test2/_doc/my_id?pipeline=geoip-info
{
  "source": {
  "ip": "8.8.8.8"
  }
}

I assume this is also the reason why the Filebeat data never gets GeoIP information.

As far as I can tell I'm following the defaults provided (Filebeat's own default IIS module) and the documentation as found in the manual.

Am I missing something or is the documentation/default module wrong?