@Override
            public <T> Optional<T> lookupOptional(Class<T> type) {
                try {
                    return Optional.of(injector.getInstance(type));
                } catch (DIException e) {
                    return Optional.empty();
                }
            }

            @Override
            public <T> Optional<T> lookupOptional(Class<T> type, String name) {

    public <T> T lookup(Class<T> type, String name) {
        return null;
    }

    @Override
    public <T> Optional<T> lookupOptional(Class<T> type) {
        return Optional.empty();
    }

    @Override
    public <T> Optional<T> lookupOptional(Class<T> type, String name) {
        return Optional.empty();
    }

    @Override
    public <T> List<T> lookupList(Class<T> type) {
        return List.of();
    }

                throws InvalidVersionSpecificationException {
            ArtifactSpec dep = createArtifactSpec(id, version, scope, artifact.getScope(), optional);
            return addDependency(dep);
        }

        public ArtifactSpec addDependency(String id, String version, boolean optional)
                throws InvalidVersionSpecificationException {

            throws InvalidVersionSpecificationException {
        VersionRange versionRange = VersionRange.createFromVersionSpec(version);

        return artifactFactory.createDependencyArtifact(
                GROUP_ID, id, versionRange, "jar", null, scope, inheritedScope, optional);
    }

import java.io.File;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.stream.Collectors;

import org.apache.maven.api.*;
import org.apache.maven.api.services.DependencyResolver;
import org.apache.maven.api.services.DependencyResolverResult;

            Artifact artifact = (Artifact) iter.next();
            System.out.println("Artifact: " + artifact.getDependencyConflictId() + " " + artifact.getVersion()
                    + " Optional=" + (artifact.isOptional() ? "true" : "false"));
            assertTrue(
                    artifact.getVersion().equals("1.0"), "Incorrect version for " + artifact.getDependencyConflictId());
        }
    }

     * <p>
     * Effective properties are computed from system, user and optionally project properties, layered with
     * defined precedence onto each other to achieve proper precedence. Precedence is defined as:
     * <ul>
     *     <li>System properties (lowest precedence)</li>
     *     <li>Project properties (optional)</li>
     *     <li>User properties (highest precedence)</li>
     * </ul>

            Artifact artifact = (Artifact) iter.next();
            System.out.println("Artifact: " + artifact.getDependencyConflictId() + " " + artifact.getVersion()
                    + " Optional=" + (artifact.isOptional() ? "true" : "false"));
            assertTrue(
                    artifact.getVersion().equals("1.0"), "Incorrect version for " + artifact.getDependencyConflictId());
        }
    }

        }

        @Override
        public Optional<Lifecycle> lookup(String id) {
            return Optional.empty();
        }
    };

    private static final PackagingRegistry emptyPackagingRegistry = new PackagingRegistry() {
        @Override
        public Optional<Packaging> lookup(String id) {
            return Optional.of(new Packaging() {
                @Override

            <multiplicity>*</multiplicity>
          </association>
        </field>
        <field>
          <name>optional</name>
          <version>4.0.0+</version>
          <description>
            Indicates the dependency is optional for use of this library. While the
            version of the dependency will be taken into account for dependency calculation if the