private static final Artifact SENTINEL = new DefaultArtifact("org.apache.maven.banned:user-relocation:1.0");

    @Override
    public Artifact relocatedTarget(
            RepositorySystemSession session, ArtifactDescriptorResult artifactDescriptorResult, Model model)
            throws ArtifactDescriptorException {
        Relocations relocations = (Relocations) session.getData()

            throws ArtifactDescriptorException {
        Artifact result = null;
        for (MavenArtifactRelocationSource source : artifactRelocationSources.values()) {
            result = source.relocatedTarget(session, artifactDescriptorResult, model);
            if (result != null) {
                break;
            }
        }
        return result;
    }

    private void missingDescriptor(