message: Check if :id has valid format for mongoId
diff: @@ -162,7 +162,7 @@ export class CourseController {
  * @apiError NotFoundError Includes implicit authorization check. (In getCourse helper method.)
  * @apiError ForbiddenError (Redundant) Authorization check.
  */
  - @Get('/:id')
  + @Get('/:id([a-fA-F0-9]{24})')
  async getCourseView(@Param('id') id: string, @CurrentUser() currentUser: IUser): Promise<ICourseView> {
  const course = await this.getCourse(id, currentUser);
  