Map<C, V> row = safeGet(rowMap(), rowKey);
    return row != null && Maps.safeContainsKey(row, columnKey);
  }

  @Override
  public @Nullable V get(@Nullable Object rowKey, @Nullable Object columnKey) {
    Map<C, V> row = safeGet(rowMap(), rowKey);
    return (row == null) ? null : safeGet(row, columnKey);
  }

  @Override
  public boolean isEmpty() {
    return size() == 0;
  }

     *
     * @param message The message describing the problem, may be {@code null}.
     * @param severity The severity level of the problem, may be {@code null} to default to
     *            {@link SettingsProblem.Severity#ERROR}.
     * @param source A hint about the source of the problem like a file path, may be {@code null}.
     * @param lineNumber The one-based index of the line containing the problem or {@code -1} if unknown.

        if (reporting == null) {
            return;
        }

        Build build = model.getBuild();

        if (build == null) {
            build = new Build();
            model.setBuild(build);
            model.setLocation("build", location);
        }

        Plugin sitePlugin = findSitePlugin(build);

        if (sitePlugin == null) {
            sitePlugin = new Plugin();

        repos.add(artifactRepositoryFactory.createArtifactRepository(
                "repo1", "string://url1", new ArtifactRepositoryLayoutStub(), null, null));
        repos.add(artifactRepositoryFactory.createArtifactRepository(
                "repo2", "string://url2", new ArtifactRepositoryLayoutStub(), null, null));

        StringWagon wagon = (StringWagon) wagonManager.getWagon("string");

@GwtCompatible
final class CollectPreconditions {

  static void checkEntryNotNull(@Nullable Object key, @Nullable Object value) {
    if (key == null) {
      throw new NullPointerException("null key in entry: null=" + value);
    } else if (value == null) {
      throw new NullPointerException("null value in entry: " + key + "=null");
    }
  }

  @CanIgnoreReturnValue
  static int checkNonnegative(int value, String name) {
    if (value < 0) {

  public void testOffer_nullSupported() {
    assertTrue("offer(null) should return true", getQueue().offer(null));
    expectAdded((E) null);
  }

  @CollectionFeature.Require(value = SUPPORTS_ADD, absent = ALLOWS_NULL_VALUES)
  public void testOffer_nullUnsupported() {
    assertThrows(NullPointerException.class, () -> getQueue().offer(null));
    expectUnchanged();

        if (activation == null) {
            return false;
        }

        ActivationProperty property = activation.getProperty();

        if (property == null) {
            return false;
        }

        String name = property.getName();
        boolean reverseName = false;

        if (name != null && name.startsWith("!")) {
            reverseName = true;

        if (kid == null) {
            return;
        }

        if (children == null) {
            children = new MetadataTreeNode[nChildren];
        }

        children[index % nChildren] = kid;
    }

    // ------------------------------------------------------------------
    @Override
    public String toString() {
        return md == null ? "no metadata" : md.toString();
    }

     * @return The property, or null if no such property exists.
     */
    public PropertyMetaData findProperty(String name) {
        PropertyMetaData propertyMetaData = declaredProperties.get(name);
        if (propertyMetaData != null) {
            return propertyMetaData;
        }
        ClassMetaData superClass = getSuperClass();
        if (superClass != null) {
            return superClass.findProperty(name);

     * created automatically.
     *
     * @param output The file to serialize the model to, must not be {@code null}.
     * @param options The options to use for serialization, may be {@code null} to use the default values.
     * @param model The model to serialize, must not be {@code null}.
     * @throws IOException If the model could not be serialized.
     */