if (stack == null || stack.isEmpty()) {
            throw new IllegalStateException();
        }
        return stack.getFirst();
    }

    public void exit() throws MojoExecutionException {
        final LinkedList<ScopeState> stack = values.get();
        if (stack == null || stack.isEmpty()) {
            throw new IllegalStateException();
        }
        stack.removeFirst();
        if (stack.isEmpty()) {

            String currentJavaVersion = System.getProperty("java.version");
            if (!matchesVersion(requiredJavaVersion, currentJavaVersion)) {
                throw new IllegalStateException("Required Java version " + requiredJavaVersion
                        + " is not met by current version: " + currentJavaVersion);
            }
        }
    }

        String resource = "/org/apache/maven/model/pom-" + v + ".xml";
        URL url = getClass().getResource(resource);
        if (url == null) {
            throw new IllegalStateException("The super POM " + resource + " was not found"
                    + ", please verify the integrity of your Maven installation");
        }
        try (InputStream is = url.openStream()) {

            private void doLoadFullReactor() {
                Path rootDirectory;
                try {
                    rootDirectory = request.getSession().getRootDirectory();
                } catch (IllegalStateException e) {
                    // if no root directory, bail out
                    return;
                }
                List<Path> toLoad = new ArrayList<>();

    public void checkPrerequisites(PluginDescriptor pluginDescriptor) throws PluginIncompatibleException {
        List<IllegalStateException> prerequisiteExceptions = new ArrayList<>();
        prerequisitesCheckers.forEach(c -> {
            try {
                c.accept(pluginDescriptor);
            } catch (IllegalStateException e) {
                prerequisiteExceptions.add(e);
            }
        });

    }

    static void associate(org.eclipse.aether.RepositorySystemSession rsession, Session session) {
        if (!rsession.getData().set(InternalSession.class, null, from(session))) {
            throw new IllegalStateException("A maven session is already associated with the repository session");
        }
    }

    RemoteRepository getRemoteRepository(org.eclipse.aether.repository.RemoteRepository repository);

        @Override
        public String getUserProperty(String key) {
            return null;
        }

        @Override
        public Model getRawModel(Path from, String groupId, String artifactId) throws IllegalStateException {
            throw new UnsupportedOperationException();
        }

        @Override
        public Model getRawModel(Path from, Path p) {
            throw new UnsupportedOperationException();
        }

                    return 1; // 1.1 > 1-sp

                case LIST_ITEM:
                    return 1; // 1.1 > 1-1

                default:
                    throw new IllegalStateException("invalid item: " + item.getClass());
            }
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }

                                + requiredMavenVersion,
                        e);
                return;
            }
            if (!isRequirementMet) {
                throw new IllegalStateException("Required Maven version " + requiredMavenVersion
                        + " is not met by current version " + runtimeInformation.getMavenVersion());
            }
        }
    }

        Objects.requireNonNull(projectRealm, "projectRealm cannot be null");

        if (cache.containsKey(key)) {
            throw new IllegalStateException("Duplicate project realm for extensions " + key);
        }

        CacheRecord record = new CacheRecord(projectRealm, extensionArtifactFilter);

        cache.put(key, record);

        return record;