return null;
    }
    V value = map.remove(columnKey);
    if (map.isEmpty()) {
      backingMap.remove(rowKey);
    }
    return value;
  }

  @CanIgnoreReturnValue
  private Map<R, V> removeColumn(@Nullable Object column) {
    Map<R, V> output = new LinkedHashMap<>();
    Iterator<Entry<R, Map<C, V>>> iterator = backingMap.entrySet().iterator();
    while (iterator.hasNext()) {