* {@code get(null)}, {@code keySet().contains(null)} or {@code remove(null)}.
   */
  ALLOWS_NULL_KEY_QUERIES,
  ALLOWS_NULL_KEYS(ALLOWS_NULL_KEY_QUERIES),
  /**
   * The map does not throw {@code NullPointerException} on calls such as {@code
   * containsValue(null)}, {@code values().contains(null)} or {@code values().remove(null)}.
   */
  ALLOWS_NULL_VALUE_QUERIES,

    /**
     * 引数が<code>null</code>でないことを表明します。
     *
     * @param argName
     *            {@code null} であってはならない引数の名前
     * @param argValue
     *            引数の値
     * @throws NullArgumentException
     *             引数が<code>null</code>の場合。
     */
    public static void assertArgumentNotNull(final String argName, final Object argValue) {
        if (argValue == null) {

        String groupId = model.getGroupId();
        if (groupId == null && model.getParent() != null) {
            groupId = model.getParent().getGroupId();
        }
        return groupId;
    }

    private String getVersion(Model model) {
        String version = model.getVersion();
        if (version == null && model.getParent() != null) {
            version = model.getParent().getVersion();
        }

     * used by plugins.
     *
     * @param artifacts The set of artifacts, may be {@code null}.
     */
    public void setResolvedArtifacts(Set<Artifact> artifacts) {
        this.resolvedArtifacts = (artifacts != null) ? artifacts : Collections.<Artifact>emptySet();
        this.artifacts = null;
        this.artifactMap = null;
    }

    /**

        if (reporting != null) {
            reporting.setOutputDirectory(alignToBaseDirectory(reporting.getOutputDirectory(), basedir));
        }
    }

    public String alignToBaseDirectory(String path, File basedir) {
        if (basedir == null) {
            return path;
        }

        if (path == null) {
            return null;
        }

        String s = stripBasedirToken(path);

        InputStream inputStream = request.getInputStream();
        if (path == null && url == null && reader == null && inputStream == null) {
            throw new IllegalArgumentException("path, url, reader or inputStream must be non null");
        }
        try {
            InputSource source = null;
            if (request.getModelId() != null || request.getLocation() != null) {
                source = new InputSource(

                            valueClass == null ? null : valueClass.getName(), valueClass == null ? null : valueClass.getClassLoader(),
                            value, targetClass == null ? null : targetClass.getName(),
                            targetClass == null ? null : targetClass.getClassLoader()),
                    e);
        }
    }

    /**
     * インスタンスフィールドかどうか返します。

        // v1-->v2
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.1", true, null, null, 2, 1));
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.2", true, null, null, 2, 2));

        // v1-->v3
        graph.addEdge(v1, v3, new MetadataGraphEdge("1.1", true, null, null, 2, 1));
        graph.addEdge(v1, v3, new MetadataGraphEdge("1.2", true, null, null, 4, 2));

        // v3-->v4

        PersistedToolchains global = readToolchains(globalSource, request, problems);

        Source userSource = request.getUserToolchainsSource().orElse(null);
        PersistedToolchains user = readToolchains(userSource, request, problems);

        PersistedToolchains effective = toolchainsMerger.merge(user, global, false, null);

        if (hasErrors(problems)) {

        ClassRealm pluginRealm = pluginDescriptor.getClassRealm();

        if (pluginRealm == null) {
            try {
                setupPluginRealm(pluginDescriptor, session, null, null, null);
            } catch (PluginResolutionException e) {
                String msg = "Cannot setup plugin realm [mojoDescriptor=" + mojoDescriptor.getId()