`UnmodifiableMultimap.forEach` uses the `Multimap.forEach` default implementation which involves listing entries, and creating a new lambda instead of simply passing the BiConsumer through to the protected instance. This is safe to pass directly though because `forEach(BiConsumer)` is a read-only operation.
abstract Multimap<K, V> multimap();
    @Override
    public int size() {
      return multimap().size();
    }
    @Override
    public boolean contains(@Nullable Object o) {
      if (o instanceof Map.Entry) {
        Map.Entry<?, ?> entry = (Map.Entry<?, ?>) o;
        return multimap().containsEntry(entry.getKey(), entry.getValue());
      }
      return false;
    }
    @Override
    public boolean remove(@Nullable Object o) {
      if (o instanceof Map.Entry) {
        Map.Entry<?, ?> entry = (Map.Entry<?, ?>) o;
        return multimap().remove(entry.getKey(), entry.getValue());
      }
      return false;
    }
    @Override
    public void clear() {
      multimap().clear();
    }
  }
  
  static final class AsMap<K, V> extends Maps.ViewCachingAbstractMap<K, Collection<V>> {