Add a workaround for null values in the tag list

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

docker/docker_image.go

@@ -91,6 +91,12 @@ func GetRepositoryTags(ctx context.Context, sys *types.SystemContext, ref types.
  }
  for _, tag := range tagsHolder.Tags {
  if _, err := reference.WithTag(dr.ref, tag); err != nil { // Ensure the tag does not contain unexpected values
+ // Per https://github.com/containers/skopeo/issues/2409 , unknown versions of Sonatype Nexus , contrary
+ // to the spec, include JSON null values in the list; and Go silently parses them as "".
+ if tag == "" {
+ logrus.Debugf("Ignoring invalid empty tag")
+ continue
+ }
  // Per https://github.com/containers/skopeo/issues/2346 , unknown versions of JFrog Artifactory,
  // contrary to the tag format specified in
  // https://github.com/opencontainers/distribution-spec/blob/8a871c8234977df058f1a14e299fe0a673853da2/spec.md?plain=1#L160 ,