Collector.of(
          () -> new ToOptionalState<>(null),
          ToOptionalState::add,
          ToOptionalState::combine,
          ToOptionalState::getOptional,
          Collector.Characteristics.UNORDERED);

  /**
   * A collector that converts a stream of zero or one elements to an {@code Optional}.
   *

      Collector.of(
          () -> new ToOptionalState<>(null),
          ToOptionalState::add,
          ToOptionalState::combine,
          ToOptionalState::getOptional,
          Collector.Characteristics.UNORDERED);

  /**
   * A collector that converts a stream of zero or one elements to an {@code Optional}.
   *

     * The value is computed during the dependencies collection phase.
     *
     * @return {@code true} if the dependency is optional, or {@code false} if mandatory
     * @see DependencyCoordinates#getOptional()
     */
    boolean isOptional();

    /**
     * {@return coordinates with the same identifiers as this dependency}.
     */
    @Nonnull
    @Override
    DependencyCoordinates toCoordinates();

                        dependency = dependency.withScope(managedDependency.getScope());
                    }
                    if (dependency.getOptional() == null && managedDependency.getOptional() != null) {
                        dependency = dependency.withOptional(managedDependency.getOptional());
                    }
                    if (dependency.getExclusions().isEmpty()

            exclusions.add(convert(exclusion));
        }

        return new Dependency(
                artifact,
                dependency.getScope(),
                dependency.getOptional() != null ? dependency.isOptional() : null,
                exclusions);
    }

    private Exclusion convert(org.apache.maven.model.Exclusion exclusion) {

                .collect(Collectors.toList());

        return new Dependency(
                artifact,
                dependency.getScope(),
                dependency.getOptional() != null ? dependency.isOptional() : null,
                exclusions);
    }

    private static Exclusion toExclusion(org.apache.maven.model.Exclusion exclusion) {

    public boolean isOptional() {
        return (getOptional() != null) ? Boolean.parseBoolean(getOptional()) : false;
    }

            ]]>
          </code>
        </codeSegment>
        <codeSegment>
          <version>4.0.0/4.0.99</version>
          <code>
            <![CDATA[
    public void setOptional(boolean optional) {
        setOptional(String.valueOf(optional));
    }

            if (request.getValidationLevel() >= ModelBuildingRequest.VALIDATION_LEVEL_MAVEN_2_0) {
                validateBoolean(
                        prefix, "optional", problems, errOn30, Version.V20, d.getOptional(), d.getManagementKey(), d);

                if (!management) {
                    validateVersion(
                            prefix, "version", problems, errOn30, Version.V20, d.getVersion(), d.getManagementKey(), d);

    interface Parameters : ValueSourceParameters {

        @get:Optional
        val buildTimestampFromBuildReceipt: Property<String>

        @get:Optional
        val buildTimestampFromGradleProperty: Property<String>

        @get:Optional
        val enableConfigurationCacheForDocsTests: Property<Boolean>

        val runningOnCi: Property<Boolean>

    @get:Input
    @get:Optional
    abstract val commitId: Property<String>

    @get:Input
    @get:Optional
    abstract val scriptTemplateCommitId: Property<String>

    @get:Input
    abstract val snapshot: Property<Boolean>

    @get:Input
    abstract val promotionBuild: Property<Boolean>

    @get:Input
    @get:Optional
    abstract val buildTimestamp: Property<Date>