newEntryArray[outI++] = entry;
      }
      entryArray = newEntryArray;
    }
    return new JdkBackedImmutableMap<>(delegateMap, ImmutableList.asImmutableList(entryArray, n));
  }

  private final transient Map<K, V> delegateMap;
  private final transient ImmutableList<Entry<K, V>> entries;

  JdkBackedImmutableMap(Map<K, V> delegateMap, ImmutableList<Entry<K, V>> entries) {
    this.delegateMap = delegateMap;

import java.util.Map;

/**
 * GWT emulation of {@link JdkBackedImmutableMap}. Never used, but must exist so that the client is
 * willing to deserialize maps that were this type on the server.
 */
@ElementTypesAreNonnullByDefault
final class JdkBackedImmutableMap<K, V> extends ForwardingImmutableMap<K, V> {
  JdkBackedImmutableMap(Map<? extends K, ? extends V> delegate) {
    super(delegate);
  }

  @GwtIncompatible // SerializableTester
  public void testKeySetIsSerializable_jdkBackedImmutableMap() {
    class NonSerializableClass {}

    Entry<String, NonSerializableClass>[] entries =
        arrayOf(ImmutableMap.entryOf("one", new NonSerializableClass()));

    ImmutableMap<String, NonSerializableClass> map =
        JdkBackedImmutableMap.create(1, entries, /* throwIfDuplicateKeys= */ true);
    Set<String> set = map.keySet();

          Entry<K, V> onlyEntry = requireNonNull(entries[0]);
          return of(onlyEntry.getKey(), onlyEntry.getValue());
        default:
          entriesUsed = true;
          return JdkBackedImmutableMap.create(size, entries, /* throwIfDuplicateKeys= */ true);
      }
    }

    private static <K, V> Entry<K, V>[] lastEntryForEachKey(Entry<K, V>[] entries, int size) {
      Set<K> seen = new HashSet<>();