AsMap(Map<K, Collection<V>> submap) {
      this.submap = submap;
    }

    @Override
    protected Set<Entry<K, Collection<V>>> createEntrySet() {
      return new AsMapEntries();
    }

    // The following methods are included for performance.

    @Override
    public boolean containsKey(@Nullable Object key) {
      return Maps.safeContainsKey(submap, key);
    }