public final class ImmutableClassToInstanceMap<B>
    extends ForwardingMap<Class<? extends @NonNull B>, B>
    implements ClassToInstanceMap<B>, Serializable {

  private static final ImmutableClassToInstanceMap<Object> EMPTY =
      new ImmutableClassToInstanceMap<>(ImmutableMap.<Class<?>, Object>of());

  /**
   * Returns an empty {@code ImmutableClassToInstanceMap}.
   *

    assertSame(
        ImmutableClassToInstanceMap.of(),
        SerializableTester.reserialize(ImmutableClassToInstanceMap.of()));
  }

  public void testCopyOf_map_empty() {
    Map<Class<?>, Object> in = emptyMap();
    ClassToInstanceMap<Object> map = ImmutableClassToInstanceMap.copyOf(in);
    assertTrue(map.isEmpty());
    assertSame(map, ImmutableClassToInstanceMap.of());

import java.util.Set;
import org.jspecify.annotations.NonNull;
import org.jspecify.annotations.Nullable;

/**
 * A mutable class-to-instance map backed by an arbitrary user-provided map. See also {@link
 * ImmutableClassToInstanceMap}.
 *
 * <p>See the Guava User Guide article on <a href=
 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#classtoinstancemap">{@code
 * ClassToInstanceMap}</a>.
 *
 * @author Kevin Bourrillion