}

            @Nonnull
            @Override
            public Optional<Source> getGlobalToolchainsSource() {
                return Optional.ofNullable(globalToolchainsSource);
            }

            @Nonnull
            @Override
            public Optional<Source> getUserToolchainsSource() {
                return Optional.ofNullable(userToolchainsSource);
            }
        }
    }

      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>1.2.6</version>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>logkit</groupId>
      <artifactId>logkit</artifactId>
      <version>1.0.1</version>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>

@Experimental
public interface ArtifactManager extends Service {

    /**
     * Returns the path of the file previously associated to this artifact
     * or {@code Optional.empty()} if no path has been associated.
     */
    @Nonnull
    Optional<Path> getPath(@Nonnull Artifact artifact);

    /**
     * Associates the given file path to the artifact.
     */
    void setPath(@Nonnull Artifact artifact, Path path);

    BeanConfigurationRequest setClassLoader(ClassLoader classLoader);

    /**
     * Gets the optional preprocessor for configuration values.
     *
     * @return The preprocessor for configuration values or {@code null} if none.
     */
    BeanConfigurationValuePreprocessor getValuePreprocessor();

    /**
     * Sets the optional preprocessor for configuration values.
     *

                    .collect(Collectors.toMap(t -> t.id(), t -> t));
        }

        @Override
        public Optional<T> lookup(String id) {
            return Optional.ofNullable(values.get(id));
        }
    }

  <dependencies>
    <dependency>
      <groupId>maven-test</groupId>
      <artifactId>t07-d</artifactId>
      <version>1.1</version>
      <type>jar</type>
      <scope>compile</scope>
      <optional>true</optional>
    </dependency>
  </dependencies>

        return delegate.getExecutionId();
    }

    @Override
    public String getGoal() {
        return delegate.getGoal();
    }

    @Override
    public Optional<XmlNode> getConfiguration() {
        return Optional.of(delegate.getConfiguration()).map(Xpp3Dom::getDom);
    }

    @Override
    public String toString() {
        return delegate.toString();
    }

    </dependency>
    <dependency>
      <groupId>maven-test</groupId>
      <artifactId>t08-d</artifactId>
      <version>1.1</version>
      <type>jar</type>
      <scope>compile</scope>
      <optional>false</optional>
    </dependency>
  </dependencies>

    </dependency>
    <dependency>
      <groupId>maven-test</groupId>
      <artifactId>t08-d</artifactId>
      <version>1.1</version>
      <type>jar</type>
      <scope>compile</scope>
      <optional>false</optional>
    </dependency>
  </dependencies>

      </dependency>
      <dependency>
        <groupId>maven-test</groupId>
        <artifactId>t07-d</artifactId>
        <version>1.2</version>
        <scope>test</scope>
        <optional>false</optional>
      </dependency>
    </dependencies>
  </dependencyManagement>