constructor (undoManager) {
    this.undoManager_ = undoManager
    this.currentBatchCommand_ = null
    this.batchCommandStack_ = []
  }
@param {history.UndoManager|null} undoManager - The undo manager.
    A value of `null` is valid for cases where no history recording is required.
    See singleton: {@link module:history.HistoryRecordingService.HistoryRecordingService.NO_HISTORY}