/**
 * The annotated element can be {@code null}.
 *
 * @see Nonnull
 * @since 4.0.0
 */
@Experimental
@Documented
@Retention(RetentionPolicy.CLASS)

     * @return the merged node
     */
    @Nullable
    static XmlNode merge(@Nullable XmlNode dominant, @Nullable XmlNode recessive) {
        return merge(dominant, recessive, null);
    }

    @Nullable
    static XmlNode merge(
            @Nullable XmlNode dominant, @Nullable XmlNode recessive, @Nullable Boolean childMergeOverride) {
        if (recessive == null) {
            return dominant;
        }

import org.apache.maven.api.annotations.Nullable;

/**
 * An XML reader request.
 *
 * @since 4.0.0
 */
@Experimental
@Immutable
public interface XmlReaderRequest {

    @Nullable
    Path getPath();

    @Nullable
    URL getURL();

    @Nullable
    InputStream getInputStream();

    @Nullable
    Reader getReader();

    @Nullable
    Transformer getTransformer();

     */
    @Nonnull
    Optional<Source> getUserToolchainsSource();

    @Nonnull
    static ToolchainsBuilderRequest build(
            @Nonnull Session session, @Nullable Source globalToolchainsSource, @Nullable Source userToolchainsSource) {
        return builder()
                .session(nonNull(session, "session cannot be null"))
                .globalToolchainsSource(globalToolchainsSource)

         * found at the given file or in the given directory.
         *
         * @since 4.0.0
         */
        @Nullable
        Path locateExistingPom(@Nonnull Path project);
    }

    @Nullable
    ModelSource resolve(@Nonnull ModelLocator modelLocator, @Nonnull String relative);

    @Nonnull
    static ModelSource fromPath(@Nonnull Path path) {

     */
    <T> boolean replace(@Nonnull Key<T> key, @Nullable T oldValue, @Nullable T newValue);

    /**
     * Gets the session data associated with the specified key.
     *
     * @param key the key for which to retrieve the session data, must not be {@code null}
     * @return the session data associated with the key or {@code null} if none
     */
    @Nullable
    <T> T get(@Nonnull Key<T> key);

    /**

import org.apache.maven.api.annotations.Nonnull;
import org.apache.maven.api.annotations.Nullable;

/**
 * An XML writer request.
 *
 * @since 4.0.0
 * @param <T> the object type to read
 */
@Experimental
public interface XmlWriterRequest<T> {

    @Nullable
    Path getPath();

    @Nullable
    OutputStream getOutputStream();

    @Nullable
    Writer getWriter();

    @Nonnull
    T getContent();

 */
@Experimental
@Immutable
@Provider
public interface Node {

    /**
     * @return artifact for this node
     */
    @Nullable
    Artifact getArtifact();

    /**
     * @return dependency for this node
     */
    @Nullable
    Dependency getDependency();

    /**
     * Gets the child nodes of this node.
     *
     * @return the child nodes of this node, never {@code null}
     */

                return new Exclusion() {
                    @Nullable
                    @Override
                    public String getGroupId() {
                        return exclusion.getGroupId();
                    }

                    @Nullable
                    @Override
                    public String getArtifactId() {

    ModelResolver getModelResolver();

    @Nonnull
    ModelRepositoryHolder getModelRepositoryHolder();

    @Nullable
    ModelCache getModelCache();

    @Nullable
    Object getListener();

    @Nullable
    ModelBuilderResult getInterimResult();

    @Nullable
    ModelTransformerContextBuilder getTransformerContextBuilder();

    @Nonnull