polic_get_brs looks for buildroots or build in given policy data. applyVolumePolicy just fetches the buildinfo and it refers to archives which don't have buildroots. BuildTagTest then uses this data to get build_tag, build_tags or buildroots from rpms/archives. None of these is present for image by default.

Solution seems to be to get taskinfo for given build and look for build target /build tag there. Any better solutions?

E.g. https://koji.fedoraproject.org/koji/buildinfo?buildID=1508281 doesn't have archives with buildroots

...
 {'btype': 'image',
  'btype_id': 4,
  'build_id': 1508281,
  'buildroot_id': None,
  'checksum': '8b9d6be18b834b435ba8f01515073df8',
  'checksum_type': 0,
  'extra': None,
  'filename': 'fedora-container-base-minimal.ks',
  'id': 338301,
  'metadata_only': False,
  'size': 2250,
  'type_description': 'Kickstart',
  'type_extensions': 'ks',
  'type_id': 24,
  'type_name': 'ks'},
...