*
   * @throws IllegalArgumentException if the stream consists of two or more elements.
   * @throws NullPointerException if any element in the stream is {@code null}.
   * @return {@code Optional.of(onlyElement)} if the stream has exactly one element (must not be
   *     {@code null}) and returns {@code Optional.empty()} if it has none.
   */
  @SuppressWarnings("unchecked")
  public static <T> Collector<T, ?, Optional<T>> toOptional() {

                }));
    expectReplacement(entry(getKeyForNullValue(), v3()));
  }

  @MapFeature.Require({SUPPORTS_PUT, ALLOWS_NULL_KEYS})
  public void testMergeAbsentNullKey() {
    assertEquals(
        "Map.merge(null, value, function) should return value",
        v3(),
        getMap()
            .merge(
                null,
                v3(),

    public void test_nullHandling() {
        // Test with null ParseException
        QueryParseException queryParseException = new QueryParseException(null);
        assertNotNull(queryParseException);
        assertNull(queryParseException.getCause());
        // getMessage() may return null when constructed with null
        // This is expected behavior for exceptions with null cause
    }

    public void test_nestedCause() {

     * Constructs an instance.
     *
     * @param clazz
     *            the class (must not be {@literal null})
     */
    public ClassIterator(final Class<?> clazz) {
        this(clazz, true);
    }

    /**
     * Constructs an instance.
     *
     * @param clazz the class (must not be {@literal null})
     * @param includeObject if {@literal true}, includes the {@link Object} class in the iteration
     */

     * @param keyList The list of keys to register this extractor under.
     */
    public void register(final List<String> keyList) {
        if (keyList == null || keyList.isEmpty()) {
            throw new IllegalArgumentException("keyList must not be null or empty.");
        }
        getExtractorFactory().addExtractor(keyList, this);
    }

    /**
     * Returns the MimeTypeHelper instance from the CrawlerContainer.

     */
    public PACDecodingException() {
        this(null, null);
    }

    /**
     * Constructs a new PAC decoding exception with the specified detail message.
     * @param message the detail message
     */
    public PACDecodingException(final String message) {
        this(message, null);
    }

    /**
     * Constructs a new PAC decoding exception with the specified cause.

import org.codelibs.fess.unit.UnitFessTestCase;

public class SystemUtilTest extends UnitFessTestCase {

    public void test_getSearchEngineHttpAddress_null() {
        // Clear the system property to test null case
        String originalValue = System.getProperty(Constants.FESS_SEARCH_ENGINE_HTTP_ADDRESS);
        System.clearProperty(Constants.FESS_SEARCH_ENGINE_HTTP_ADDRESS);

        try {

					<fmt:formatDate value="${fe:parseDate(doc.last_modified)}" type="BOTH" pattern="yyyy-MM-dd HH:mm" />
					<c:if test="${doc.last_modified==null || doc.last_modified==''}">
						<fmt:formatDate value="${fe:parseDate(doc.created)}" type="BOTH" pattern="yyyy-MM-dd HH:mm" />
					</c:if>
					<c:if test="${doc.content_length!=null && doc.content_length!=''}">
						<div class="d-sm-none"></div>
						<span class="d-none d-sm-inline-block">&nbsp;</span>

    }

    /**
     * Test that assertPropertyNotNull throws exception for null input
     */
    public void test_assertPropertyNotNull_withNull() {
        try {
            // Create a test instance that extends FessLabels
            TestFessLabels labels = new TestFessLabels();
            labels.testAssertPropertyNotNull(null);
            fail("Should throw IllegalArgumentException");

      return spliterator.tryAdvance(action);
    }

    @Override
    @Nullable GeneralSpliterator<E> trySplit() {
      Spliterator<E> split = spliterator.trySplit();
      return split == null ? null : new GeneralSpliteratorOfObject<>(split);
    }
  }

  @IgnoreJRERequirement // *should* be redundant with the annotation on SpliteratorTester
  private static final class GeneralSpliteratorOfPrimitive<