skip_on_empty doesn't work if the value is an empty array

I have been scratching my head over this issue. The source sometimes has a blank offers, sometimes it is an array with data and sometimes it is an empty array - like this one:
https://api.hel.fi/linkedevents/v1/event/matko:16134/

With the latter example I was getting a bunch of Array index missing, extraction failed exceptions from the extract plugin, despite the skip_on_empty plugin running before, as you can see from my yml file:

  field_offers_is_free:
    -
      plugin: skip_on_empty
      method: process
      source: offers
    -
      plugin: extract
      index:
        - 0
        - is_free
  field_offers_info_url:
    -
      plugin: skip_on_empty
      method: process
      source: offers
    -
      plugin: extract
      default: false
      index:
        - 0
        - info_url
        - fi

I managed - in the end - to track down the reason for why our skip_on_empty plugin was never called: When Get sets $multiple to true, processRow in MigrateExecutable runs a foreach on the value - causing the whole skip_on_empty plugin to be skipped.

With this quick fix in modules/migrate/src/Plugin/migrate/process/Get.php's transform function things work fine for me:

    if (is_string($source)) {
      $a = is_array($return[0]);
      $b = !empty($return[0]);
      $this->multiple = $a && $b;
      return $return[0];
    }

Did I encounter a bug in Migrate or should I change my migration configuration?