if (cacheRecord != null && cacheRecord.getException() != null) {
            throw cacheRecord.getException();
        }

        return cacheRecord;
    }

    @Override
    public CacheRecord put(Key key, List<Artifact> pluginArtifacts) {
        Objects.requireNonNull(pluginArtifacts, "pluginArtifacts cannot be null");

        assertUniqueKey(key);

     *            information along, may be <code>null</code>.
     */
    public void merge(Model target, Model source, boolean sourceDominant, Map<?, ?> hints) {
        Objects.requireNonNull(target, "target cannot be null");

        if (source == null) {
            return;
        }

        Map<Object, Object> context = new HashMap<>();
        if (hints != null) {
            context.putAll(hints);
        }

        if (settings.isUsePluginRegistry()) {
            addViolation(problems, Severity.WARNING, "usePluginRegistry", null, "is deprecated and has no effect.");
        }

        List<String> pluginGroups = settings.getPluginGroups();

        if (pluginGroups != null) {
            for (int i = 0; i < pluginGroups.size(); i++) {
                String pluginGroup = pluginGroups.get(i).trim();

                Prerequisites prerequisites =
                        mavenProject.getModel().getDelegate().getPrerequisites();
                if (prerequisites != null && prerequisites.getMaven() != null) {
                    logger.warn(
                            "The project {} uses prerequisites"
                                    + " which is only intended for maven-plugin projects "

  * When annotating existing internal code, use `org.jetbrains.annotations.Contract`, e.g. `@Contract(null -> null; !null -> !null)`.
      When doing so, still annotate nullable parameters and the return type as `@Nullable`.
  * Do not use `@Contract` for public APIs.
  * For polynull public APIs, the solution has to be decided on a case-by-case basis.

Do not remove `null` checks on public API boundaries, even if the annotations (or rather lack of them) suggest this.

      int size = (keyList == null) ? 0 : keyList.count;
      checkPositionIndex(index, size);
      if (index >= (size / 2)) {
        previous = (keyList == null) ? null : keyList.tail;
        nextIndex = size;
        while (index++ < size) {
          previous();
        }
      } else {
        next = (keyList == null) ? null : keyList.head;
        while (index-- > 0) {
          next();

        current.elemCount = 0;
        // Also clear these fields so that one deleted Entry doesn't retain all elements.
        current.left = null;
        current.right = null;
        current.pred = null;
        current.succ = null;

        current = next;
      }
      successor(header, header);
      rootReference.clear();
    } else {

      Set<Object> keys = cache.asMap().keySet();
      assertThat(keys.remove(null)).isFalse();
      assertThat(keys.remove(6)).isFalse();
      assertThat(keys.remove(-6)).isFalse();
      assertThat(keys.removeAll(asList(null, 0, 15, 1500))).isFalse();
      assertThat(keys.retainAll(asList(null, 0, 15, 1500))).isFalse();
      checkEmpty(keys);
      checkEmpty(cache);
    }
  }

      Set<Object> keys = cache.asMap().keySet();
      assertThat(keys.remove(null)).isFalse();
      assertThat(keys.remove(6)).isFalse();
      assertThat(keys.remove(-6)).isFalse();
      assertThat(keys.removeAll(asList(null, 0, 15, 1500))).isFalse();
      assertThat(keys.retainAll(asList(null, 0, 15, 1500))).isFalse();
      checkEmpty(keys);
      checkEmpty(cache);
    }
  }

        PlexusConfiguration[] ces = c.getChildren();
        if (ces != null) {
            for (PlexusConfiguration ce : ces) {
                String value = ce.getValue(null);
                String defaultValue = ce.getAttribute("default-value", null);
                if (value != null || defaultValue != null) {
                    XmlNode e = XmlNode.newInstance(
                            ce.getName(),