return checkNotNull(delegate);
  }

  private static class UnmodifiableMultimap<K extends @Nullable Object, V extends @Nullable Object>
      extends ForwardingMultimap<K, V> implements Serializable {
    final Multimap<K, V> delegate;
    @LazyInit @CheckForNull transient Collection<Entry<K, V>> entries;
    @LazyInit @CheckForNull transient Multiset<K> keys;