message: Refactor UnitController using orFail for unit 404
diff: @@ -14,10 +14,7 @@ import {IUser} from '../../../shared/models/IUser';
  export class UnitController {
  protected static async getUnitFor (unitId: string, currentUser: IUser, privilege: 'userCanViewCourse' | 'userCanEditCourse') {
  - const unit = await Unit.findById(unitId);
  - if (!unit) {
  - throw new NotFoundError();
  - }
  + const unit = await Unit.findById(unitId).orFail(new NotFoundError());
  const course = await Course.findById(unit._course);
  if (!course.checkPrivileges(currentUser)[privilege]) {
  