public List<Artifact> getMissingArtifacts() {
        return missingArtifacts == null ? Collections.emptyList() : Collections.unmodifiableList(missingArtifacts);
    }

    public MetadataResolutionResult addMissingArtifact(Artifact artifact) {
        missingArtifacts = initList(missingArtifacts);

        missingArtifacts.add(artifact);

        return this;
    }