network stack is offline.

  [[3]] "Remote" repositories referenced using the file:// protocol may
        be available. However, if that file:// url references a
        file-share, as in the case of an NFS or SMB mount, that will
        be unavailable.

  So, offline mode has several implications, some of which may not be
  altogether obvious:

     * @param artifactId never {@code null}
     * @param version can be {@code null}
     * @return the matching model or {@code null}
     * @throws IllegalStateException if version was null and multiple modules share the same groupId + artifactId
     */
    public Model get(String groupId, String artifactId, String version) {
        return modelsByGa.getOrDefault(new GAKey(groupId, artifactId), Collections.emptySet()).stream()

            if (relocatedArtifact != null) {
                if (withinSameGav(relocatedArtifact, a)) {
                    result.setArtifact(relocatedArtifact);
                    return model; // they share same model
                } else {
                    result.addRelocation(a);
                    a = relocatedArtifact;
                    result.setArtifact(a);
                }
            } else {

            } else {
                repoMetadata.setMetadata(metadata);
                setRepository = true;
            }
        }
        return setRepository;
    }

    /*
     * TODO share with DefaultPluginMappingManager.
     */
    protected Metadata readMetadata(File mappingFile) throws RepositoryMetadataReadException {

        try (InputStream in = Files.newInputStream(mappingFile.toPath())) {