*/
    @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();

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

                    @Nullable
                    @Override
                    public String getArtifactId() {

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

/**
 * Describes a problem that was encountered during project building. A problem can either be an exception that was
 * thrown or a simple string message. In addition, a problem carries a hint about its source.
 *

 * <p>
 * Annotated fields must not be null after construction has completed.
 * <p>
 * When this annotation is applied to a method it applies to the method return value.
 *
 * @see Nullable
 * @since 4.0.0
 */
@Experimental
@Documented
@Retention(RetentionPolicy.CLASS)
@Target({ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD})

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

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

/**
 * Centralized class for Maven Core feature information.
 * Features configured are supposed to be final in a given maven session.
 *
 * @since 4.0.0
 */
public final class Features {

    /**
     * Name of the Maven user property to enable or disable the build/consumer POM feature.
     */

    }

    private Exclusion toExclusion(org.eclipse.aether.graph.Exclusion exclusion) {
        return new Exclusion() {
            @Nullable
            @Override
            public String getGroupId() {
                return exclusion.getGroupId();
            }

            @Nullable
            @Override
            public String getArtifactId() {
                return exclusion.getArtifactId();
            }