}
    } else if (collection.add(value)) {
      totalSize++;
      return true;
    } else {
      return false;
    }
  }

  private Collection<V> getOrCreateCollection(@ParametricNullness K key) {
    Collection<V> collection = map.get(key);
    if (collection == null) {
      collection = createCollection(key);
      map.put(key, collection);
    }
    return collection;