* @param supplier the supplier will compute the new value
     * @return the session data associated with the key
     */
    @Nullable
    <T> T computeIfAbsent(@Nonnull Key<T> key, @Nonnull Supplier<T> supplier);

    /**
     * Create a key using the given class as an identifier and as the type of the object.
     */
    static <T> Key<T> key(Class<T> clazz) {
        return new Key<>(clazz, clazz);
    }

    /**

                    return;
                }
            }
        }
        throw new IllegalArgumentException(message);
    }

    public static Map<String, Artifact> artifactMapByVersionlessId(Collection<Artifact> artifacts) {
        Map<String, Artifact> artifactMap = new LinkedHashMap<>();

        if (artifacts != null) {
            for (Artifact artifact : artifacts) {

        assertTrue(range.containsVersion(new DefaultArtifactVersion("1.1-SNAPSHOT")));
        assertTrue(range.containsVersion(new DefaultArtifactVersion("1.2-SNAPSHOT")));

        range = VersionRange.createFromVersionSpec("[1.0-SNAPSHOT,1.2]");

        assertTrue(range.containsVersion(new DefaultArtifactVersion("1.0-SNAPSHOT")));
        assertTrue(range.containsVersion(new DefaultArtifactVersion("1.1-SNAPSHOT")));
    }

        boolean missing = event.getFile() == null;
        if (missing) {
            // missing artifact - let's track the path anyway
            File dir = event.getSession().getLocalRepository().getBasedir();
            dir = new File(
                    dir, event.getSession().getLocalRepositoryManager().getPathForLocalArtifact(event.getArtifact()));
            trackingDir = dir.getParentFile().toPath().resolve(".tracking");
        } else {

        Build build = new Build();
        build.setDirectory(expected.substring(0, expected.length() - "/classes".length()));

        Model model = new Model();
        model.setBuild(build);

        MavenProject project = new MavenProject(model);
        project.setFile(new File("pom.xml").getCanonicalFile());

        Set<Artifact> reversedArtifacts = new LinkedHashSet<>(4);
        artifacts.add(new DefaultArtifact("g", "a4", "v", "compile", "jar", "", null));
        artifacts.add(new DefaultArtifact("g", "a3", "v", "compile", "jar", "", null));
        artifacts.add(new DefaultArtifact("g", "a2", "v", "compile", "jar", "", null));
        artifacts.add(new DefaultArtifact("g", "a1", "v", "compile", "jar", "", null));

        Settings settings = new Settings();
        Mirror mirror = new Mirror();
        mirror.setId("local");
        settings.addMirror(mirror);
        mirror = new Mirror();
        mirror.setId("illegal\\:/chars");
        mirror.setUrl("http://void");
        mirror.setMirrorOf("void");
        settings.addMirror(mirror);

        SimpleProblemCollector problems = new SimpleProblemCollector();

        return container;
    }

    protected File getProject(String name) throws Exception {
        File source = new File(new File(getBasedir(), getProjectsDirectory()), name);
        File target = new File(new File(getBasedir(), "target"), name);
        FileUtils.copyDirectoryStructureIfModified(source, target);
        return new File(target, "pom.xml");
    }

    public ArtifactRepository buildArtifactRepository(Repository repository) throws InvalidRepositoryException {
        return new MavenArtifactRepository(
                repository.getId(),
                repository.getUrl(),
                new DefaultRepositoryLayout(),
                new ArtifactRepositoryPolicy(),
                new ArtifactRepositoryPolicy());
    }

    private final List<Problem> problems;

    private String source;

    DefaultProblemCollector(List<Problem> problems) {
        this.problems = (problems != null) ? problems : new ArrayList<>();
    }

    @Override
    public List<Problem> getProblems() {
        return problems;
    }

    @Override
    public void setSource(String source) {
        this.source = source;
    }