public void testCheckNotNull_simple_failure() {
    assertThrows(NullPointerException.class, () -> checkNotNull(null));
  }

  public void testCheckNotNull_simpleMessage_success() {
    String result = checkNotNull(NON_NULL_STRING, IGNORE_ME);
    assertSame(NON_NULL_STRING, result);
  }

  public void testCheckNotNull_simpleMessage_failure() {
    NullPointerException expected =

  private enum ExceptionTypePolicy {

    /**
     * Exceptions should be {@link NullPointerException} or {@link UnsupportedOperationException}.
     */
    NPE_OR_UOE() {
      @Override
      public boolean isExpectedType(Throwable cause) {
        return cause instanceof NullPointerException
            || cause instanceof UnsupportedOperationException;
      }
    },

    /**

   * Stream.of(stream1, stream2, ...).flatMap(s -> s)}. If the sources are iterables, use {@code
   * Stream.of(iter1, iter2, ...).flatMap(Streams::stream)}.
   *
   * @throws NullPointerException if any of the provided iterables is {@code null}
   * @since 20.0
   */
  @SafeVarargs
  public static <T extends @Nullable Object> FluentIterable<T> concat(
      Iterable<? extends T>... inputs) {

    }

    @Test
    @DisplayName("Constructor should handle null parent")
    void testConstructor_NullParent_ThrowsNPE() {
        // When & Then: Null parent should cause NullPointerException
        assertThrows(NullPointerException.class, () -> new NetServerEnumIterator(null, treeHandle, "*", 0, null));
    }

    @Test
    @DisplayName("Constructor should handle null tree handle")

   * the call to {@code contains(null)} is permitted to throw a {@code NullPointerException}.
   *
   * @param message message to use upon assertion failure
   */
  protected void expectNullKeyMissingWhenNullKeysUnsupported(String message) {
    try {
      assertFalse(message, getMap().containsKey(null));
    } catch (NullPointerException tolerated) {
      // Tolerated
    }
  }

  /**

  private enum ExceptionTypePolicy {

    /**
     * Exceptions should be {@link NullPointerException} or {@link UnsupportedOperationException}.
     */
    NPE_OR_UOE() {
      @Override
      public boolean isExpectedType(Throwable cause) {
        return cause instanceof NullPointerException
            || cause instanceof UnsupportedOperationException;
      }
    },

    /**

    }
    expectUnchanged();
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_KEYS)
  public void testPutIfAbsent_nullKeyUnsupported() {
    assertThrows(NullPointerException.class, () -> getMap().putIfAbsent(null, v3()));
    expectUnchanged();
    expectNullKeyMissingWhenNullKeysUnsupported(
        "Should not contain null key after unsupported putIfAbsent(null, value)");
  }

        .inOrder();
  }

  public void testToMap_nullKey() {
    assertThrows(
        NullPointerException.class, () -> fluent(1, null, 2).toMap(Functions.constant("foo")));
  }

  public void testToMap_nullValue() {
    assertThrows(NullPointerException.class, () -> fluent(1, 2, 3).toMap(Functions.constant(null)));
  }

  public void testIndex() {

    expectAdded((E) null);
  }

  @CollectionFeature.Require(value = SUPPORTS_ADD, absent = ALLOWS_NULL_VALUES)
  public void testOffer_nullUnsupported() {
    assertThrows(NullPointerException.class, () -> getQueue().offer(null));
    expectUnchanged();
    expectNullMissingWhenNullUnsupported("Should not contain null after unsupported offer(null)");
  }

     * Returns the value of a specific attribute.
     *
     * @param name the name of the attribute to retrieve
     * @return the attribute value, or {@code null} if the attribute doesn't exist
     * @throws NullPointerException if name is null
     */
    @Nullable
    String attribute(@Nonnull String name);

    /**
     * Returns an immutable list of all child nodes.
     *