@Test
    void testMergeModel_ModelVersion() {
        Model parent = Model.newBuilder().modelVersion("4.0.0").build();
        Model model = Model.newInstance();
        Model.Builder builder = Model.newBuilder(model);
        modelMerger.mergeModel_ModelVersion(builder, model, parent, false, null);
        assertNull(builder.build().getModelVersion());

        model = Model.newBuilder().modelVersion("5.0.0").build();

        private volatile boolean set;
        private volatile Model model;

        Holder() {}

        Holder(Model model) {
            this.model = Objects.requireNonNull(model);
            this.set = true;
        }

        public static Model deref(Holder holder) {
            return holder != null ? holder.get() : null;
        }

        public Model get() {
            if (!set) {

/**
 * A test which demonstrates maven's recursive inheritance where
 * a distinct value is taken from each parent contributing to
 * the final model of the project being assembled. There is no
 * overriding going on amongst the models being used in this test:
 * each model in the lineage is providing a value that is not present
 * anywhere else in the lineage. We are just making sure that values

import org.apache.maven.api.services.ModelProblem;

/**
 * Collects the output of the model builder.
 *
 */
class DefaultModelBuilderResult implements ModelBuilderResult {
    private Model fileModel;
    private Model activatedFileModel;

    private Model effectiveModel;

    private List<String> modelIds;

    private Map<String, Model> rawModels;

    private Map<String, List<Profile>> activePomProfiles;

            Model model = new Model();
            model.setModelVersion("4.0.0");
            model.setGroupId(groupId);
            model.setArtifactId(artifactId);
            model.setVersion(version);
            model.setBuild(new Build());
            project = new MavenProject(model);
        }

        public ProjectBuilder setGroupId(String groupId) {

import org.apache.maven.artifact.InvalidRepositoryException;
import org.apache.maven.bridge.MavenRepositorySystem;
import org.apache.maven.model.Dependency;
import org.apache.maven.model.Parent;
import org.apache.maven.model.resolution.ModelResolver;
import org.apache.maven.model.resolution.UnresolvableModelException;
import org.eclipse.aether.DefaultRepositorySystemSession;
import org.eclipse.aether.RepositorySystem;

     *
     * @return The assembled model, never {@code null}.
     */
    @Nonnull
    Model getEffectiveModel();

    /**
     * Gets the specified raw model as it was read from a model source. Apart from basic validation, a raw model has not
     * undergone any updates by the model builder, e.g. reflects neither inheritance nor interpolation. The model

 *
 */
public class ModelResolverException extends MavenException {

    /**
     * The group id of the unresolvable model.
     */
    private final String groupId;

    /**
     * The artifact id of the unresolvable model.
     */
    private final String artifactId;

    /**
     * The version of the unresolvable model.
     */
    private final String version;

                .computeIfAbsent(profiles, l -> doInjectProfiles(model, profiles));
        return result == KEY ? model : result;
    }

    private Model doInjectProfiles(Model model, List<Profile> profiles) {
        Model orgModel = model;
        for (Profile profile : profiles) {
            if (profile != null) {

     *
     * @param model The model into which to merge the values specified by its plugin management section, must not be
     *            <code>null</code>.
     * @param request The model building request that holds further settings, must not be {@code null}.
     * @param problems The container used to collect problems that were encountered, must not be {@code null}.
     */