message: Start implementation of file unit migration
diff: // tslint:disable:no-console
  import * as mongoose from 'mongoose';
  -import {ObjectID} from 'bson';
  import {IUnitModel} from '../../models/units/Unit';
  -import {ITaskUnitModel} from '../../models/units/TaskUnit';
  -import {ITaskUnit} from '../../../../shared/models/units/ITaskUnit';
  -import {ITask} from '../../../../shared/models/task/ITask';
  -import {IUnit} from '../../../../shared/models/units/IUnit';
  +import {ObjectID} from 'bson';
  const unitSchema = new mongoose.Schema({
  _course: {
  @@ -80,6 +76,17 @@ class FileUnitMigration {
  async up() {
  console.log('FileUnit up was called');
  + try {
  + const fileUnits = await Unit.find({'__t': 'file'}).exec();
  + const updatedFileUnits = await Promise.all(fileUnits.map(async (fileUnit) => {
  + if (fileUnit._id instanceof ObjectID) {
  + const fileUnitObj = fileUnit.toObject();
  + }
  + }));
  + } catch (error) {
  + console.log(error);
  + }
  + return true;
  }
  down() {
  