snapcraft list-revisions requires a base in the API payload

The schema documented at https://dashboard.snapcraft.io/docs/v2/en/snaps.html#snap-releases for "revisions" defines that "base" is required, but snaps with no base error as exposed on https://forum.snapcraft.io/t/snapcraft-list-revisions/21110, extracted here:

$ snapcraft list-revisions kubelet
Sorry, an error occurred in Snapcraft:
None is not of type 'string'

Failed validating 'type' in schema['properties']['revisions']['items']['properties']['base']:
    {'introduced_at': 1, 'type': 'string'}

On instance['revisions'][15]['base']:
    None