if (g.getVertices().size() == 1) {
            return g;
        }

        List<MetadataGraphVertex> visited = new ArrayList<>(g.getVertices().size());
        visit(g.getEntry(), visited, g);

        List<MetadataGraphVertex> dropList = new ArrayList<>(g.getVertices().size());

        // collect drop list
        for (MetadataGraphVertex v : g.getVertices()) {

                                BuilderProblem.Severity.WARNING));
                        return value;
                    }
                })
                .visit(toolchains);
    }

    /**
     * Collects the output of the toolchains builder.
     *
     */
    static class DefaultToolchainsBuilderResult implements ToolchainsBuilderResult {

        InnerInterpolator innerInterpolator = createInterpolator(valueSources, postProcessors, request, problems);

        return new MavenTransformer(innerInterpolator::interpolate).visit(model);
    }

    private InnerInterpolator createInterpolator(
            List<? extends ValueSource> valueSources,
            List<? extends InterpolationPostProcessor> postProcessors,

            } else {
                ClasspathGraphVisitor v = new ClasspathGraphVisitor(cleanGraph, cpc);
                MetadataGraphVertex entry = cleanGraph.getEntry();
                // entry point
                v.visit(entry);
            }

            return cpc;
        } catch (GraphConflictResolutionException e) {
            throw new MetadataGraphTransformationException(e);
        }
    }

    /**
     * Traverses this node and potentially its children using the specified visitor.
     *
     * @param visitor the visitor to call back, must not be {@code null}
     * @return {@code true} to visit siblings nodes of this node as well, {@code false} to skip siblings
     */
    boolean accept(@Nonnull NodeVisitor visitor);

    /**
     * Returns a new tree starting at this node, filtering the children.

                                BuilderProblem.Severity.WARNING));
                        return value;
                    }
                })
                .visit(settings);
    }

    @Override
    public List<BuilderProblem> validate(Settings settings, boolean isProjectSettings) {
        ArrayList<BuilderProblem> problems = new ArrayList<>();

 *
 * @since 4.0.0
 */
@Experimental
@Consumer
public interface NodeVisitor {
    /**
     * Starts the visit to the specified dependency node.
     *
     * @param node the dependency node to visit
     * @return <code>true</code> to visit the specified dependency node's children, <code>false</code> to skip the
     *         specified dependency node's children and proceed to its next sibling
     */