@GwtCompatible
@ElementTypesAreNonnullByDefault
public abstract class ForwardingSortedMap<K extends @Nullable Object, V extends @Nullable Object>
    extends ForwardingMap<K, V> implements SortedMap<K, V> {
  // TODO(lowasser): identify places where thread safety is actually lost

  /** Constructor for use by subclasses. */
  protected ForwardingSortedMap() {}

  @Override
  protected abstract SortedMap<K, V> delegate();

  @Override
  @CheckForNull