_clone() {
    if (!this[OBJECT_ID]) {
      throw new RangeError('clone() requires the objectId to be set')
    }
    return instantiateTable(this[OBJECT_ID], copyObject(this.entries), copyObject(this.opIds))
  }
Returns a shallow clone of this object. This clone is used while applying
a patch to the table, and `freeze()` is called on it when we have finished
applying the patch.