}

    @Override
    public @Nullable V remove(@Nullable Object key) {
      updateBackingRowMapField();
      if (backingRowMap == null) {
        return null;
      }
      V result = Maps.safeRemove(backingRowMap, key);
      maintainEmptyInvariant();
      return result;
    }

    @Override
    public void clear() {
      updateBackingRowMapField();
      if (backingRowMap != null) {

    }
  }

  /** Removes all values for the provided key. */
  private void removeValuesForKey(@Nullable Object key) {
    Collection<V> collection = Maps.safeRemove(map, key);

    if (collection != null) {
      int count = collection.size();
      collection.clear();
      totalSize -= count;
    }
  }