*/
  public static <A extends @Nullable Object, B extends @Nullable Object, C extends @Nullable Object>
      Function<A, C> compose(Function<B, C> g, Function<A, ? extends B> f) {
    return new FunctionComposition<>(g, f);
  }

  private static final class FunctionComposition<
          A extends @Nullable Object, B extends @Nullable Object, C extends @Nullable Object>
      implements Function<A, C>, Serializable {

import org.jspecify.annotations.Nullable;

/**
 * Derived suite generators, split out of the suite builders so that they are available to GWT.
 *
 * @author George van den Driessche
 */
@GwtCompatible
@NullMarked
public final class DerivedCollectionGenerators {
  public static class MapEntrySetGenerator<K extends @Nullable Object, V extends @Nullable Object>

    public @Nullable E higher(@ParametricNullness E e) {
      return delegate.higher(e);
    }

    @Override
    public @Nullable E pollFirst() {
      throw new UnsupportedOperationException();
    }

    @Override
    public @Nullable E pollLast() {
      throw new UnsupportedOperationException();
    }

    @LazyInit private transient @Nullable UnmodifiableNavigableSet<E> descendingSet;

    return delegate.isEmpty();
  }

  @Override
  public final boolean containsKey(@Nullable Object key) {
    return Maps.safeContainsKey(delegate, key);
  }

  @Override
  public final boolean containsValue(@Nullable Object value) {
    return delegate.containsValue(value);
  }

  @Override
  public @Nullable V get(@Nullable Object key) {
    return (key == null) ? null : Maps.safeGet(delegate, key);
  }

    TreeMultimap<@Nullable String, @Nullable Integer> multimap = createPopulate();
    assertThat(multimap.entries())
        .containsExactly(
            Maps.<@Nullable String, Integer>immutableEntry(null, 7),
            Maps.<@Nullable String, Integer>immutableEntry(null, 3),
            Maps.<@Nullable String, Integer>immutableEntry(null, 1),
            Maps.<String, @Nullable Integer>immutableEntry("tree", null),

                "Method com.example.Source.baz(java.lang.String): Return nullability changed from null-unmarked to non-nullable",
            )
            assertHasNoInformation()
        }
    }

    @Test
    fun `from null-unmarked returning to nullable returning is breaking`() {

        checkNotBinaryCompatibleJava(
            v1 = """

  @Override
  public Comparator<? super E> comparator() {
    return comparator;
  }

  @Override
  public @Nullable Entry<E> firstEntry() {
    Iterator<Entry<E>> entryIterator = entryIterator();
    return entryIterator.hasNext() ? entryIterator.next() : null;
  }

  @Override
  public @Nullable Entry<E> lastEntry() {
    Iterator<Entry<E>> entryIterator = descendingEntryIterator();

  private final boolean hasLowerBound;
  private final @Nullable T lowerEndpoint;
  private final BoundType lowerBoundType;
  private final boolean hasUpperBound;
  private final @Nullable T upperEndpoint;
  private final BoundType upperBoundType;

  private GeneralRange(
      Comparator<? super T> comparator,
      boolean hasLowerBound,
      @Nullable T lowerEndpoint,
      BoundType lowerBoundType,

    return (Collector) TO_OPTIONAL;
  }

  private static final Object NULL_PLACEHOLDER = new Object();

  private static final Collector<@Nullable Object, ?, @Nullable Object> ONLY_ELEMENT =
      Collector.<@Nullable Object, ToOptionalState<Object>, @Nullable Object>of(
          () -> new ToOptionalState<>(null),
          (state, o) -> state.add((o == null) ? NULL_PLACEHOLDER : o),
          ToOptionalState::combine,

  @VisibleForTesting
  static final class ValueEntry<K extends @Nullable Object, V extends @Nullable Object>
      extends SimpleImmutableEntry<K, V> {
    final int smearedValueHash;

    @Nullable ValueEntry<K, V> nextInValueBucket;

    private @Nullable ValueEntry<K, V> predecessorInValueSet;
    private @Nullable ValueEntry<K, V> successorInValueSet;

    private @Nullable ValueEntry<K, V> predecessorInMultimap;